Patchwork RFC: Always-on elision with per-process opt-in using tunables.

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Submitter Stefan Liebler
Date May 12, 2017, 11:13 a.m.
Message ID <584704cb-644d-e06f-c1de-0bb76ca6c4cb@linux.vnet.ibm.com>
Download mbox | patch
Permalink /patch/20425/
State New
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Comments

Stefan Liebler - May 12, 2017, 11:13 a.m.
On 05/11/2017 05:45 PM, Carlos O'Donell wrote:
> I am going to propose the following:
>
> * Always build with elision support.
>
> * Elision disabled by default at runtime.
>
> * Use tunables to allow processes to opt-in to transparent elision.
>
> The benefit is that the elision support doesn't bit-rot, and we keep
> it working, and that distributions can conservatively backport elision
> and allow users to test enablement on a per-process basis.
This is an improvement for users as they can simply compare performance 
of their workload with or without lock elsion.
With (c) - see below - further tuning is possible.

>
> The elision is enabled with:
>
> GLIBC_TUNABLE=glibc.elision.enable=1
>
> The obvious set of patches are:
>
> (a) Split out some cleanups in this patch.
> (b) Always build with elision and us tunables to opt-in.
> (c) Extend tunables to allow modification of elision parameters
>     (useful for upcoming rwlock elision re-enablement).
>
> I'm testing this on x86_64, ppc64le, and s390x.
>
I've applied this patch to test on s390x.
Some changes are needed in order to build it.

Please remove the line "enable-lock-elision = @enable_lock_elision"
in config.make.in.  This variable is used in
sysdeps/unix/sysv/linux/s390/Makefile, which has to be adjusted, too:
ifeq ($(enable-lock-elision),yes)
...
endif

The s390 configure check to test the availability of __builtin_tbegin
has to be adjusted:



> diff --git a/sysdeps/unix/sysv/linux/powerpc/elision-conf.c b/sysdeps/unix/sysv/linux/powerpc/elision-conf.c
> index f631f0a..a767a0c 100644
> --- a/sysdeps/unix/sysv/linux/powerpc/elision-conf.c
> +++ b/sysdeps/unix/sysv/linux/powerpc/elision-conf.c
> @@ -21,6 +21,7 @@
>  #include <elision-conf.h>
>  #include <unistd.h>
>  #include <dl-procinfo.h>
> +#include <elf/dl-tunables.h>
>
>  /* Reasonable initial tuning values, may be revised in the future.
>     This is a conservative initial value.  */
> @@ -54,18 +55,47 @@ int __pthread_force_elision attribute_hidden;
>
>  /* Initialize elision.  */
>
> +static inline void
> +do_set_elision_enable (bool elision_enable)
> +{
> +  /* If elision is not enabled, or we are in a secure mode,
> +     make sure elision is never used...  */
> +  if (!elision_enable || __libc_enable_secure)
> +    {
> +      __pthread_force_elision = 0;
> +      return;
> +    }
> +
> +  /* ... otherwise enable elision based on hardare availability.  */
> +  __pthread_force_elision = (GLRO (dl_hwcap2)
> +			     & PPC_FEATURE2_HAS_HTM) ? 1 : 0;
> +}
> +
> +#if HAVE_TUNABLES
> +/* The elision->enable tunable is either 0 or 1 to indicate that
> +   elision should be disabled or enabled respectively.  Availability at
> +   the hardware level will still dictate if the feature is used.  */
> +void
> +DL_TUNABLE_CALLBACK (set_elision_enable) (tunable_val_t *elision_enable)
tunable_val_t *valp instead of tunable_val_t *elision_enable.

> +{
> +  int32_t elision_enable = (int32_t) valp->numval;
> +  do_set_elision_enable (elision_enable ? true : false);
> +}
> +#endif
> +
>  static void
>  elision_init (int argc __attribute__ ((unused)),
>  	      char **argv  __attribute__ ((unused)),
>  	      char **environ)
>  {
> -#ifdef ENABLE_LOCK_ELISION
> -  int elision_available = (GLRO (dl_hwcap2) & PPC_FEATURE2_HAS_HTM) ? 1 : 0;
> -  __pthread_force_elision = __libc_enable_secure ? 0 : elision_available;
> +#if HAVE_TUNABLES
> +  /* Elision depends on tunables to enable and tune elision at runtime.  */
> +# define TUNABLE_NAMESPACE elision
> +  TUNABLE_SET_VAL_WITH_CALLBACK (enable, NULL, set_elision_enable);
> +#else
> +  /* Disable elision when built without tunables.  */
> +  do_set_elision_enable (false);
>  #endif
> -  if (!__pthread_force_elision)
> -    /* Disable elision on rwlocks.  */
> -    __elision_aconf.try_tbegin = 0;
>  }
>
>  #ifdef SHARED
> diff --git a/sysdeps/unix/sysv/linux/powerpc/force-elision.h b/sysdeps/unix/sysv/linux/powerpc/force-elision.h
> index 318f791..d1feeeb 100644
> --- a/sysdeps/unix/sysv/linux/powerpc/force-elision.h
> +++ b/sysdeps/unix/sysv/linux/powerpc/force-elision.h
> @@ -16,7 +16,6 @@
>     License along with the GNU C Library; if not, see
>     <http://www.gnu.org/licenses/>.  */
>
> -#ifdef ENABLE_LOCK_ELISION
>  /* Automatically enable elision for existing user lock kinds.  */
>  #define FORCE_ELISION(m, s)						\
>    if (__pthread_force_elision						\
> @@ -25,4 +24,3 @@
>        mutex->__data.__kind |= PTHREAD_MUTEX_ELISION_NP;			\
>        s;								\
>      }
> -#endif
> diff --git a/sysdeps/unix/sysv/linux/s390/elision-conf.c b/sysdeps/unix/sysv/linux/s390/elision-conf.c
> index cc0fdef..c6d9962 100644
> --- a/sysdeps/unix/sysv/linux/s390/elision-conf.c
> +++ b/sysdeps/unix/sysv/linux/s390/elision-conf.c
> @@ -21,6 +21,7 @@
>  #include <elision-conf.h>
>  #include <unistd.h>
>  #include <dl-procinfo.h>
> +#include <elf/dl-tunables.h>
>
>  /* Reasonable initial tuning values, may be revised in the future.
>     This is a conservative initial value.  */
> @@ -55,16 +56,46 @@ int __pthread_force_elision attribute_hidden = 0;
>
>  /* Initialize elison.  */
>
> +static inline void
> +do_set_elision_enable (bool elision_enable)
> +{
> +  /* If elision is not enabled, or we are in a secure mode,
> +     make sure elision is never used...  */
> +  if (!elision_enable || __libc_enable_secure)
> +    {
> +      __pthread_force_elision = 0;
> +      return;
> +    }
> +
> +  /* ... otherwise enable elision based on hardare availability.  */
> +  __pthread_force_elision = (GLRO (dl_hwcap) & HWCAP_S390_TE) ? 1 : 0;
> +}
> +
> +#if HAVE_TUNABLES
> +/* The elision->enable tunable is either 0 or 1 to indicate that
> +   elision should be disabled or enabled respectively.  Availability at
> +   the hardware level will still dictate if the feature is used.  */
> +void
> +DL_TUNABLE_CALLBACK (set_elision_enable) (tunable_val_t *elision_enable)
tunable_val_t *valp instead of tunable_val_t *elision_enable.

> +{
> +  int32_t elision_enable = (int32_t) valp->numval;
> +  do_set_elision_enable (elision_enable ? true : false);
> +}
> +#endif
> +
>  static void
>  elision_init (int argc __attribute__ ((unused)),
>  	      char **argv  __attribute__ ((unused)),
>  	      char **environ)
>  {
> -  /* Set when the CPU and the kernel supports transactional execution.
> -     When false elision is never attempted.  */
> -  int elision_available = (GLRO (dl_hwcap) & HWCAP_S390_TE) ? 1 : 0;
> -
> -  __pthread_force_elision = __libc_enable_secure ? 0 : elision_available;
> +#if HAVE_TUNABLES
> +  /* Elision depends on tunables to enable and tune elision at runtime.  */
> +# define TUNABLE_NAMESPACE elision
> +  TUNABLE_SET_VAL_WITH_CALLBACK (enable, NULL, set_elision_enable);
> +#else
> +  /* Disable elision when built without tunables.  */
> +  do_set_elision_enable (false);
> +#endif
>  }
>
>  #ifdef SHARED
> diff --git a/sysdeps/unix/sysv/linux/s390/elision-conf.h b/sysdeps/unix/sysv/linux/s390/elision-conf.h
> index 3143f3b..32f0ed3 100644
> --- a/sysdeps/unix/sysv/linux/s390/elision-conf.h
> +++ b/sysdeps/unix/sysv/linux/s390/elision-conf.h
> @@ -15,7 +15,6 @@
>     You should have received a copy of the GNU Lesser General Public
>     License along with the GNU C Library; if not, see
>     <http://www.gnu.org/licenses/>.  */
> -#ifdef ENABLE_LOCK_ELISION
>  #ifndef _ELISION_CONF_H
>  #define _ELISION_CONF_H 1
>
> @@ -41,4 +40,3 @@ extern int __pthread_force_elision attribute_hidden;
>  #define HAVE_ELISION 1
>
>  #endif
> -#endif
> diff --git a/sysdeps/unix/sysv/linux/s390/force-elision.h b/sysdeps/unix/sysv/linux/s390/force-elision.h
> index 3ae3bcd..8e1e33e 100644
> --- a/sysdeps/unix/sysv/linux/s390/force-elision.h
> +++ b/sysdeps/unix/sysv/linux/s390/force-elision.h
> @@ -16,7 +16,6 @@
>     License along with the GNU C Library; if not, see
>     <http://www.gnu.org/licenses/>.  */
>
> -#ifdef ENABLE_LOCK_ELISION
>  /* Automatically enable elision for existing user lock kinds.  */
>  #define FORCE_ELISION(m, s)						\
>    if (__pthread_force_elision						\
> @@ -25,4 +24,3 @@
>        mutex->__data.__kind |= PTHREAD_MUTEX_ELISION_NP;			\
>        s;								\
>      }
> -#endif
> diff --git a/sysdeps/unix/sysv/linux/s390/lowlevellock.h b/sysdeps/unix/sysv/linux/s390/lowlevellock.h
> index 604137f..48f87a8 100644
> --- a/sysdeps/unix/sysv/linux/s390/lowlevellock.h
> +++ b/sysdeps/unix/sysv/linux/s390/lowlevellock.h
> @@ -22,7 +22,6 @@
>  #include <sysdeps/nptl/lowlevellock.h>
>
>  /* Transactional lock elision definitions.  */
> -# ifdef ENABLE_LOCK_ELISION
>  extern int __lll_timedlock_elision
>    (int *futex, short *adapt_count, const struct timespec *timeout, int private)
>    attribute_hidden;
> @@ -45,6 +44,5 @@ extern int __lll_trylock_elision(int *futex, short *adapt_count)
>    __lll_unlock_elision (&(futex), &(adapt_count), private)
>  #  define lll_trylock_elision(futex, adapt_count) \
Can you adjust the occurences of "#  define" within the old #ifdef 
ENABLE_LOCK_ELISON block to "# define".

>    __lll_trylock_elision(&(futex), &(adapt_count))
> -# endif  /* ENABLE_LOCK_ELISION */
>
>  #endif	/* lowlevellock.h */
> diff --git a/sysdeps/unix/sysv/linux/x86/elision-conf.c b/sysdeps/unix/sysv/linux/x86/elision-conf.c
> index 673b000..7d3d8fd 100644
> --- a/sysdeps/unix/sysv/linux/x86/elision-conf.c
> +++ b/sysdeps/unix/sysv/linux/x86/elision-conf.c
> @@ -21,6 +21,7 @@
>  #include <init-arch.h>
>  #include <elision-conf.h>
>  #include <unistd.h>
> +#include <elf/dl-tunables.h>
>
>  /* Reasonable initial tuning values, may be revised in the future.
>     This is a conservative initial value.  */
> @@ -52,17 +53,46 @@ int __pthread_force_elision attribute_hidden;
>
>  /* Initialize elison.  */
>
> +static inline void
> +do_set_elision_enable (bool elision_enable)
> +{
> +  /* If elision is not enabled, or we are in a secure mode,
> +     make sure elision is never used...  */
> +  if (!elision_enable || __libc_enable_secure)
> +    {
> +      __pthread_force_elision = 0;
> +      return;
> +    }
> +
> +  /* ... otherwise enable elision based on hardare availability.  */
> +  __pthread_force_elision = HAS_CPU_FEATURE (RTM);
> +}
> +
> +#if HAVE_TUNABLES
> +/* The elision->enable tunable is either 0 or 1 to indicate that
> +   elision should be disabled or enabled respectively.  Availability at
> +   the hardware level will still dictate if the feature is used.  */
> +void
> +DL_TUNABLE_CALLBACK (set_elision_enable) (tunable_val_t *valp)
> +{
> +  int32_t elision_enable = (int32_t) valp->numval;
> +  do_set_elision_enable (elision_enable ? true : false);
> +}
> +#endif
> +
>  static void
>  elision_init (int argc __attribute__ ((unused)),
>  	      char **argv  __attribute__ ((unused)),
>  	      char **environ)
>  {
> -  int elision_available = HAS_CPU_FEATURE (RTM);
> -#ifdef ENABLE_LOCK_ELISION
> -  __pthread_force_elision = __libc_enable_secure ? 0 : elision_available;
> +#if HAVE_TUNABLES
> +  /* Elision depends on tunables to enable and tune elision at runtime.  */
> +# define TUNABLE_NAMESPACE elision
> +  TUNABLE_SET_VAL_WITH_CALLBACK (enable, NULL, set_elision_enable);
> +#else
> +  /* Disable elision when built without tunables.  */
> +  do_set_elision_enable (false);
>  #endif
> -  if (!elision_available)
> -    __elision_aconf.retry_try_xbegin = 0; /* Disable elision on rwlocks */
>  }
>
>  #ifdef SHARED
> ---
>
Stefan Liebler - June 21, 2017, 7:02 a.m.
Are there any news for this?


On 05/12/2017 01:13 PM, Stefan Liebler wrote:
> On 05/11/2017 05:45 PM, Carlos O'Donell wrote:
>> I am going to propose the following:
>>
>> * Always build with elision support.
>>
>> * Elision disabled by default at runtime.
>>
>> * Use tunables to allow processes to opt-in to transparent elision.
>>
>> The benefit is that the elision support doesn't bit-rot, and we keep
>> it working, and that distributions can conservatively backport elision
>> and allow users to test enablement on a per-process basis.
> This is an improvement for users as they can simply compare performance 
> of their workload with or without lock elsion.
> With (c) - see below - further tuning is possible.
> 
>>
>> The elision is enabled with:
>>
>> GLIBC_TUNABLE=glibc.elision.enable=1
>>
>> The obvious set of patches are:
>>
>> (a) Split out some cleanups in this patch.
>> (b) Always build with elision and us tunables to opt-in.
>> (c) Extend tunables to allow modification of elision parameters
>>     (useful for upcoming rwlock elision re-enablement).
>>
>> I'm testing this on x86_64, ppc64le, and s390x.
>>
> I've applied this patch to test on s390x.
> Some changes are needed in order to build it.
> 
> Please remove the line "enable-lock-elision = @enable_lock_elision"
> in config.make.in.  This variable is used in
> sysdeps/unix/sysv/linux/s390/Makefile, which has to be adjusted, too:
> ifeq ($(enable-lock-elision),yes)
> ...
> endif
> 
> The s390 configure check to test the availability of __builtin_tbegin
> has to be adjusted:
> diff --git a/sysdeps/s390/configure.ac b/sysdeps/s390/configure.ac
> index 8a782e7..62bcfb9 100644
> --- a/sysdeps/s390/configure.ac
> +++ b/sysdeps/s390/configure.ac
> @@ -32,7 +32,7 @@ else
>   fi
>   rm -f conftest* ])
> 
> -if test "$enable_lock_elision" = yes && test 
> "$libc_cv_gcc_builtin_tbegin" = no ; then
> +if test "$libc_cv_gcc_builtin_tbegin" = no ; then
>      critic_missing="$critic_missing The used GCC has no support for 
> __builtin_tbegin, which is needed for lock-elision on target S390."
>   fi
> 
> Note: __builtin_tbegin is available on RHEL/SLES GCC 4.8.5.
> 
> 
> Please remove '--enable-lock-elision=yes' in INSTALL, too.
> 
> With these mentioned changes and the comments below,
> I could build glibc and the testsuite runs without regressions.
> 
> I've also used a small s390 specific test program to check wether a 
> mutex was elided or not:
> ./prog
> Lock was a normal lock!
> 
> GLIBC_TUNABLES=glibc.elision.enable=0 ./prog
> Lock was a normal lock!
> 
> GLIBC_TUNABLES=glibc.elision.enable=1 ./prog
> Lock was elided via a transaction! (nesting-depth=1)
> 
> GLIBC_TUNABLES=glibc.elision.enable=1 ./prog_secure
> Lock was a normal lock!
> 
> GLIBC_TUNABLES=glibc.elision.enable=2 ./prog
> Lock was a normal lock!
> 
> GLIBC_TUNABLES=glibc.elision.enable=yes ./prog
> Lock was a normal lock!
> 
> 
>> Thoughts?
>>
>> diff --git a/config.h.in b/config.h.in
>> index 2caa412..47b139e 100644
>> --- a/config.h.in
>> +++ b/config.h.in
>> @@ -147,9 +147,6 @@
>>  /* Define if __stack_chk_guard canary should be randomized at program 
>> startup.  */
>>  #undef ENABLE_STACKGUARD_RANDOMIZE
>>
>> -/* Define if lock elision should be enabled by default.  */
>> -#undef ENABLE_LOCK_ELISION
>> -
>>  /* Package description.  */
>>  #undef PKGVERSION
>>
>> diff --git a/configure b/configure
>> index 422482f..d3b68c1 100755
>> --- a/configure
>> +++ b/configure
>> @@ -677,7 +677,6 @@ enable_werror
>>  all_warnings
>>  force_install
>>  bindnow
>> -enable_lock_elision
>>  hardcoded_path_in_tests
>>  enable_timezone_tools
>>  use_default_link
>> @@ -766,7 +765,6 @@ enable_profile
>>  enable_timezone_tools
>>  enable_hardcoded_path_in_tests
>>  enable_stackguard_randomization
>> -enable_lock_elision
>>  enable_add_ons
>>  enable_hidden_plt
>>  enable_bind_now
>> @@ -1427,8 +1425,6 @@ Optional Features:
>>    --enable-stackguard-randomization
>>                            initialize __stack_chk_guard canary with a 
>> random
>>                            number at program start
>> -  --enable-lock-elision=yes/no
>> -                          Enable lock elision for pthread mutexes by 
>> default
>>    --enable-add-ons[=DIRS...]
>>                            configure and build add-ons in 
>> DIR1,DIR2,... search
>>                            for add-ons if no parameter given
>> @@ -3395,19 +3391,6 @@ if test "$enable_stackguard_randomize" = yes; then
>>
>>  fi
>>
>> -# Check whether --enable-lock-elision was given.
>> -if test "${enable_lock_elision+set}" = set; then :
>> -  enableval=$enable_lock_elision; enable_lock_elision=$enableval
>> -else
>> -  enable_lock_elision=no
>> -fi
>> -
>> -
>> -if test "$enable_lock_elision" = yes ; then
>> -  $as_echo "#define ENABLE_LOCK_ELISION 1" >>confdefs.h
>> -
>> -fi
>> -
>>  # Check whether --enable-add-ons was given.
>>  if test "${enable_add_ons+set}" = set; then :
>>    enableval=$enable_add_ons;
>> diff --git a/configure.ac b/configure.ac
>> index 7f43042..a970296 100644
>> --- a/configure.ac
>> +++ b/configure.ac
>> @@ -199,16 +199,6 @@ if test "$enable_stackguard_randomize" = yes; then
>>    AC_DEFINE(ENABLE_STACKGUARD_RANDOMIZE)
>>  fi
>>
>> -AC_ARG_ENABLE([lock-elision],
>> -          AC_HELP_STRING([--enable-lock-elision[=yes/no]],
>> -                 [Enable lock elision for pthread mutexes by default]),
>> -          [enable_lock_elision=$enableval],
>> -          [enable_lock_elision=no])
>> -AC_SUBST(enable_lock_elision)
>> -if test "$enable_lock_elision" = yes ; then
>> -  AC_DEFINE(ENABLE_LOCK_ELISION)
>> -fi
>> -
>>  dnl Generic infrastructure for drop-in additions to libc.
>>  AC_ARG_ENABLE([add-ons],
>>            AC_HELP_STRING([--enable-add-ons@<:@=DIRS...@:>@],
>> diff --git a/elf/dl-tunables.h b/elf/dl-tunables.h
>> index f33adfb..3dad518 100644
>> --- a/elf/dl-tunables.h
>> +++ b/elf/dl-tunables.h
>> @@ -18,8 +18,8 @@
>>     License along with the GNU C Library; if not, see
>>     <http://www.gnu.org/licenses/>.  */
>>
>> -#ifndef _TUNABLES_H_
>> -#define _TUNABLES_H_
>> +#ifndef _DL_TUNABLES_H_
>> +#define _DL_TUNABLES_H_
>>
>>  #if !HAVE_TUNABLES
>>  static inline void
>> diff --git a/elf/dl-tunables.list b/elf/dl-tunables.list
>> index b9f1488..97062f9 100644
>> --- a/elf/dl-tunables.list
>> +++ b/elf/dl-tunables.list
>> @@ -77,4 +77,12 @@ glibc {
>>        security_level: SXID_IGNORE
>>      }
>>    }
>> +  elision {
>> +    enable {
>> +      type: INT_32
>> +      minval: 0
>> +      maxval: 1
>> +      security_level: SXID_IGNORE
>> +    }
>> +  }
>>  }
>> diff --git a/nptl/Makefile b/nptl/Makefile
>> index 6d48c0c..a720612 100644
>> --- a/nptl/Makefile
>> +++ b/nptl/Makefile
>> @@ -704,6 +704,10 @@ $(objpfx)tst-oddstacklimit.out: 
>> $(objpfx)tst-oddstacklimit $(objpfx)tst-basic1
>>      $(evaluate-test)
>>  endif
>>
>> +# Disable elision for tst-mutex8 so it can verify error case for
>> +# destroying a mutex.
>> +tst-mutex8-ENV = GLIBC_TUNABLES=glibc.elision.enable=0
>> +
>>  # The tests here better do not run in parallel
>>  ifneq ($(filter %tests,$(MAKECMDGOALS)),)
>>  .NOTPARALLEL:
>> diff --git a/nptl/tst-mutex8.c b/nptl/tst-mutex8.c
>> index 1d288d2..ef59db5 100644
>> --- a/nptl/tst-mutex8.c
>> +++ b/nptl/tst-mutex8.c
>> @@ -127,9 +127,8 @@ check_type (const char *mas, pthread_mutexattr_t *ma)
>>        return 1;
>>      }
>>
>> -  /* Elided mutexes don't fail destroy. If elision is not explicitly 
>> disabled
>> -     we don't know, so can also not check this.  */
>> -#ifndef ENABLE_LOCK_ELISION
>> +  /* Elided mutexes don't fail destroy, but this test is run with
>> +     elision disabled so we can test them.  */
>>    e = pthread_mutex_destroy (m);
>>    if (e == 0)
>>      {
>> @@ -142,7 +141,6 @@ check_type (const char *mas, pthread_mutexattr_t *ma)
>>            mas);
>>        return 1;
>>      }
>> -#endif
>>
>>    if (pthread_mutex_unlock (m) != 0)
>>      {
>> @@ -157,7 +155,6 @@ check_type (const char *mas, pthread_mutexattr_t *ma)
>>      }
>>
>>    /* Elided mutexes don't fail destroy.  */
>> -#ifndef ENABLE_LOCK_ELISION
>>    e = pthread_mutex_destroy (m);
>>    if (e == 0)
>>      {
>> @@ -171,7 +168,6 @@ mutex_destroy of self-trylocked mutex did not 
>> return EBUSY %s\n",
>>            mas);
>>        return 1;
>>      }
>> -#endif
>>
>>    if (pthread_mutex_unlock (m) != 0)
>>      {
>> @@ -207,7 +203,6 @@ mutex_destroy of self-trylocked mutex did not 
>> return EBUSY %s\n",
>>      }
>>
>>    /* Elided mutexes don't fail destroy.  */
>> -#ifndef ENABLE_LOCK_ELISION
>>    e = pthread_mutex_destroy (m);
>>    if (e == 0)
>>      {
>> @@ -220,7 +215,6 @@ mutex_destroy of self-trylocked mutex did not 
>> return EBUSY %s\n",
>>  mutex_destroy of condvar-used mutex did not return EBUSY for %s\n", 
>> mas);
>>        return 1;
>>      }
>> -#endif
>>
>>    done = true;
>>    if (pthread_cond_signal (&c) != 0)
>> @@ -280,7 +274,6 @@ mutex_destroy of condvar-used mutex did not return 
>> EBUSY for %s\n", mas);
>>      }
>>
>>    /* Elided mutexes don't fail destroy.  */
>> -#ifndef ENABLE_LOCK_ELISION
>>    e = pthread_mutex_destroy (m);
>>    if (e == 0)
>>      {
>> @@ -295,7 +288,6 @@ mutex_destroy of condvar-used mutex did not return 
>> EBUSY for %s\n", mas);
>>            mas);
>>        return 1;
>>      }
>> -#endif
>>
>>    if (pthread_cancel (th) != 0)
>>      {
>> diff --git a/scripts/gen-tunables.awk b/scripts/gen-tunables.awk
>> index 601240a..6dba7e1 100644
>> --- a/scripts/gen-tunables.awk
>> +++ b/scripts/gen-tunables.awk
>> @@ -122,9 +122,9 @@ END {
>>    }
>>
>>    print "/* AUTOGENERATED by gen-tunables.awk.  */"
>> -  print "#ifndef _TUNABLES_H_"
>> +  print "#ifndef _DL_TUNABLES_H_"
>>    print "# error \"Do not include this file directly.\""
>> -  print "# error \"Include tunables.h instead.\""
>> +  print "# error \"Include dl-tunables.h instead.\""
>>    print "#endif"
>>
>>    # Now, the enum names
>> diff --git a/sysdeps/powerpc/nptl/elide.h b/sysdeps/powerpc/nptl/elide.h
>> index 1c42814..06986cc 100644
>> --- a/sysdeps/powerpc/nptl/elide.h
>> +++ b/sysdeps/powerpc/nptl/elide.h
>> @@ -19,7 +19,6 @@
>>  #ifndef ELIDE_PPC_H
>>  # define ELIDE_PPC_H
>>
>> -#ifdef ENABLE_LOCK_ELISION
>>  # include <htm.h>
>>  # include <elision-conf.h>
>>
>> @@ -114,12 +113,4 @@ __elide_unlock (int is_lock_free)
>>  # define ELIDE_UNLOCK(is_lock_free) \
>>    __elide_unlock (is_lock_free)
>>
>> -# else
>> -
>> -# define ELIDE_LOCK(adapt_count, is_lock_free) 0
>> -# define ELIDE_TRYLOCK(adapt_count, is_lock_free, write) 0
>> -# define ELIDE_UNLOCK(is_lock_free) 0
>> -
>> -#endif /* ENABLE_LOCK_ELISION  */
>> -
>>  #endif
>> diff --git a/sysdeps/powerpc/powerpc32/sysdep.h 
>> b/sysdeps/powerpc/powerpc32/sysdep.h
>> index f92ab2c..0ed83d3 100644
>> --- a/sysdeps/powerpc/powerpc32/sysdep.h
>> +++ b/sysdeps/powerpc/powerpc32/sysdep.h
>> @@ -88,7 +88,7 @@ GOT_LABEL:            ;                          \
>>    cfi_endproc;                                      \
>>    ASM_SIZE_DIRECTIVE(name)
>>
>> -#if ! IS_IN(rtld) && defined (ENABLE_LOCK_ELISION)
>> +#if ! IS_IN(rtld)
>>  # define ABORT_TRANSACTION \
>>      cmpwi    2,0;        \
>>      beq      1f;        \
>> diff --git a/sysdeps/powerpc/powerpc64/sysdep.h 
>> b/sysdeps/powerpc/powerpc64/sysdep.h
>> index db7c1d7..79a2697 100644
>> --- a/sysdeps/powerpc/powerpc64/sysdep.h
>> +++ b/sysdeps/powerpc/powerpc64/sysdep.h
>> @@ -272,7 +272,7 @@ LT_LABELSUFFIX(name,_name_end): ; \
>>    TRACEBACK_MASK(name,mask)    \
>>    END_2(name)
>>
>> -#if !IS_IN(rtld) && defined (ENABLE_LOCK_ELISION)
>> +#if !IS_IN(rtld)
>>  # define ABORT_TRANSACTION \
>>      cmpdi    13,0;        \
>>      beq      1f;        \
>> diff --git a/sysdeps/powerpc/sysdep.h b/sysdeps/powerpc/sysdep.h
>> index f07b959..d1a9bd9 100644
>> --- a/sysdeps/powerpc/sysdep.h
>> +++ b/sysdeps/powerpc/sysdep.h
>> @@ -21,10 +21,8 @@
>>   */
>>  #define _SYSDEPS_SYSDEP_H 1
>>  #include <bits/hwcap.h>
>> -#ifdef ENABLE_LOCK_ELISION
>>  #include <tls.h>
>>  #include <htm.h>
>> -#endif
>>
>>  #define PPC_FEATURE_970 (PPC_FEATURE_POWER4 + PPC_FEATURE_HAS_ALTIVEC)
>>
>> @@ -176,7 +174,7 @@
>>     we abort transaction just before syscalls.
>>
>>     [1] Documentation/powerpc/transactional_memory.txt [Syscalls]  */
>> -#if !IS_IN(rtld) && defined (ENABLE_LOCK_ELISION)
>> +#if !IS_IN(rtld)
>>  # define ABORT_TRANSACTION \
>>    ({                         \
>>      if (THREAD_GET_TM_CAPABLE ())        \
>> diff --git a/sysdeps/s390/nptl/bits/pthreadtypes.h 
>> b/sysdeps/s390/nptl/bits/pthreadtypes.h
>> index 48ffdb4..88d21f0 100644
>> --- a/sysdeps/s390/nptl/bits/pthreadtypes.h
>> +++ b/sysdeps/s390/nptl/bits/pthreadtypes.h
>> @@ -89,37 +89,25 @@ typedef union
>>         binary compatibility with static initializers.  */
>>      int __kind;
>>  #if __WORDSIZE == 64
>> -# ifdef ENABLE_LOCK_ELISION
>>      short __spins;
>>      short __elision;
>>      /* Mutex __spins initializer used by PTHREAD_MUTEX_INITIALIZER.  */
>> -#  define __PTHREAD_SPINS               0, 0
>> -# else
>> -    int __spins;
>> -    /* Mutex __spins initializer used by PTHREAD_MUTEX_INITIALIZER.  */
>> -#  define __PTHREAD_SPINS               0
>> -# endif
>> +# define __PTHREAD_SPINS               0, 0
>>      __pthread_list_t __list;
>>  # define __PTHREAD_MUTEX_HAVE_PREV    1
>>  #else
>>      unsigned int __nusers;
>>      __extension__ union
>>      {
>> -# ifdef ENABLE_LOCK_ELISION
>>        struct
>>        {
>>      short __espins;
>>      short __elision;
>>        } _d;
>> -#  define __spins _d.__espins
>> -#  define __elision _d.__elision
>> -    /* Mutex __spins initializer used by PTHREAD_MUTEX_INITIALIZER.  */
>> -#  define __PTHREAD_SPINS               { 0, 0 }
>> -# else
>> -      int __spins;
>> -    /* Mutex __spins initializer used by PTHREAD_MUTEX_INITIALIZER.  */
>> -#  define __PTHREAD_SPINS               0
>> -# endif
>> +# define __spins _d.__espins
>> +# define __elision _d.__elision
>> +      /* Mutex __spins initializer used by 
>> PTHREAD_MUTEX_INITIALIZER.  */
>> +# define __PTHREAD_SPINS               { 0, 0 }
>>        __pthread_slist_t __list;
>>      };
>>  #endif
> Adhemerval's commit "Move shared pthread definitions to common headers"
> consolidates the pthradtypes.h files.
> Thus sysdeps/s390/nptl/bits/pthreadtypes.h does not exist anymore.
> I've adjusted sysdeps/s390/nptl/bits/pthreadtypes-arch.h for my test:
> diff --git a/sysdeps/s390/nptl/bits/pthreadtypes-arch.h 
> b/sysdeps/s390/nptl/bits/pthreadtypes-arch.h
> index 3a9ac57..db7195a 100644
> --- a/sysdeps/s390/nptl/bits/pthreadtypes-arch.h
> +++ b/sysdeps/s390/nptl/bits/pthreadtypes-arch.h
> @@ -40,11 +40,7 @@
>   /* Definitions for internal mutex struct.  */
>   #define __PTHREAD_COMPAT_PADDING_MID
>   #define __PTHREAD_COMPAT_PADDING_END
> -#ifdef ENABLE_LOCK_ELISION
>   #define __PTHREAD_MUTEX_LOCK_ELISION    1
> -#else
> -#define __PTHREAD_MUTEX_LOCK_ELISION    0
> -#endif
> 
>   #define __LOCK_ALIGNMENT
>   #define __ONCE_ALIGNMENT
> 
> 
> 
>> diff --git a/sysdeps/unix/sysv/linux/powerpc/elision-conf.c 
>> b/sysdeps/unix/sysv/linux/powerpc/elision-conf.c
>> index f631f0a..a767a0c 100644
>> --- a/sysdeps/unix/sysv/linux/powerpc/elision-conf.c
>> +++ b/sysdeps/unix/sysv/linux/powerpc/elision-conf.c
>> @@ -21,6 +21,7 @@
>>  #include <elision-conf.h>
>>  #include <unistd.h>
>>  #include <dl-procinfo.h>
>> +#include <elf/dl-tunables.h>
>>
>>  /* Reasonable initial tuning values, may be revised in the future.
>>     This is a conservative initial value.  */
>> @@ -54,18 +55,47 @@ int __pthread_force_elision attribute_hidden;
>>
>>  /* Initialize elision.  */
>>
>> +static inline void
>> +do_set_elision_enable (bool elision_enable)
>> +{
>> +  /* If elision is not enabled, or we are in a secure mode,
>> +     make sure elision is never used...  */
>> +  if (!elision_enable || __libc_enable_secure)
>> +    {
>> +      __pthread_force_elision = 0;
>> +      return;
>> +    }
>> +
>> +  /* ... otherwise enable elision based on hardare availability.  */
>> +  __pthread_force_elision = (GLRO (dl_hwcap2)
>> +                 & PPC_FEATURE2_HAS_HTM) ? 1 : 0;
>> +}
>> +
>> +#if HAVE_TUNABLES
>> +/* The elision->enable tunable is either 0 or 1 to indicate that
>> +   elision should be disabled or enabled respectively.  Availability at
>> +   the hardware level will still dictate if the feature is used.  */
>> +void
>> +DL_TUNABLE_CALLBACK (set_elision_enable) (tunable_val_t *elision_enable)
> tunable_val_t *valp instead of tunable_val_t *elision_enable.
> 
>> +{
>> +  int32_t elision_enable = (int32_t) valp->numval;
>> +  do_set_elision_enable (elision_enable ? true : false);
>> +}
>> +#endif
>> +
>>  static void
>>  elision_init (int argc __attribute__ ((unused)),
>>            char **argv  __attribute__ ((unused)),
>>            char **environ)
>>  {
>> -#ifdef ENABLE_LOCK_ELISION
>> -  int elision_available = (GLRO (dl_hwcap2) & PPC_FEATURE2_HAS_HTM) ? 
>> 1 : 0;
>> -  __pthread_force_elision = __libc_enable_secure ? 0 : 
>> elision_available;
>> +#if HAVE_TUNABLES
>> +  /* Elision depends on tunables to enable and tune elision at 
>> runtime.  */
>> +# define TUNABLE_NAMESPACE elision
>> +  TUNABLE_SET_VAL_WITH_CALLBACK (enable, NULL, set_elision_enable);
>> +#else
>> +  /* Disable elision when built without tunables.  */
>> +  do_set_elision_enable (false);
>>  #endif
>> -  if (!__pthread_force_elision)
>> -    /* Disable elision on rwlocks.  */
>> -    __elision_aconf.try_tbegin = 0;
>>  }
>>
>>  #ifdef SHARED
>> diff --git a/sysdeps/unix/sysv/linux/powerpc/force-elision.h 
>> b/sysdeps/unix/sysv/linux/powerpc/force-elision.h
>> index 318f791..d1feeeb 100644
>> --- a/sysdeps/unix/sysv/linux/powerpc/force-elision.h
>> +++ b/sysdeps/unix/sysv/linux/powerpc/force-elision.h
>> @@ -16,7 +16,6 @@
>>     License along with the GNU C Library; if not, see
>>     <http://www.gnu.org/licenses/>.  */
>>
>> -#ifdef ENABLE_LOCK_ELISION
>>  /* Automatically enable elision for existing user lock kinds.  */
>>  #define FORCE_ELISION(m, s)                        \
>>    if (__pthread_force_elision                        \
>> @@ -25,4 +24,3 @@
>>        mutex->__data.__kind |= PTHREAD_MUTEX_ELISION_NP;            \
>>        s;                                \
>>      }
>> -#endif
>> diff --git a/sysdeps/unix/sysv/linux/s390/elision-conf.c 
>> b/sysdeps/unix/sysv/linux/s390/elision-conf.c
>> index cc0fdef..c6d9962 100644
>> --- a/sysdeps/unix/sysv/linux/s390/elision-conf.c
>> +++ b/sysdeps/unix/sysv/linux/s390/elision-conf.c
>> @@ -21,6 +21,7 @@
>>  #include <elision-conf.h>
>>  #include <unistd.h>
>>  #include <dl-procinfo.h>
>> +#include <elf/dl-tunables.h>
>>
>>  /* Reasonable initial tuning values, may be revised in the future.
>>     This is a conservative initial value.  */
>> @@ -55,16 +56,46 @@ int __pthread_force_elision attribute_hidden = 0;
>>
>>  /* Initialize elison.  */
>>
>> +static inline void
>> +do_set_elision_enable (bool elision_enable)
>> +{
>> +  /* If elision is not enabled, or we are in a secure mode,
>> +     make sure elision is never used...  */
>> +  if (!elision_enable || __libc_enable_secure)
>> +    {
>> +      __pthread_force_elision = 0;
>> +      return;
>> +    }
>> +
>> +  /* ... otherwise enable elision based on hardare availability.  */
>> +  __pthread_force_elision = (GLRO (dl_hwcap) & HWCAP_S390_TE) ? 1 : 0;
>> +}
>> +
>> +#if HAVE_TUNABLES
>> +/* The elision->enable tunable is either 0 or 1 to indicate that
>> +   elision should be disabled or enabled respectively.  Availability at
>> +   the hardware level will still dictate if the feature is used.  */
>> +void
>> +DL_TUNABLE_CALLBACK (set_elision_enable) (tunable_val_t *elision_enable)
> tunable_val_t *valp instead of tunable_val_t *elision_enable.
> 
>> +{
>> +  int32_t elision_enable = (int32_t) valp->numval;
>> +  do_set_elision_enable (elision_enable ? true : false);
>> +}
>> +#endif
>> +
>>  static void
>>  elision_init (int argc __attribute__ ((unused)),
>>            char **argv  __attribute__ ((unused)),
>>            char **environ)
>>  {
>> -  /* Set when the CPU and the kernel supports transactional execution.
>> -     When false elision is never attempted.  */
>> -  int elision_available = (GLRO (dl_hwcap) & HWCAP_S390_TE) ? 1 : 0;
>> -
>> -  __pthread_force_elision = __libc_enable_secure ? 0 : 
>> elision_available;
>> +#if HAVE_TUNABLES
>> +  /* Elision depends on tunables to enable and tune elision at 
>> runtime.  */
>> +# define TUNABLE_NAMESPACE elision
>> +  TUNABLE_SET_VAL_WITH_CALLBACK (enable, NULL, set_elision_enable);
>> +#else
>> +  /* Disable elision when built without tunables.  */
>> +  do_set_elision_enable (false);
>> +#endif
>>  }
>>
>>  #ifdef SHARED
>> diff --git a/sysdeps/unix/sysv/linux/s390/elision-conf.h 
>> b/sysdeps/unix/sysv/linux/s390/elision-conf.h
>> index 3143f3b..32f0ed3 100644
>> --- a/sysdeps/unix/sysv/linux/s390/elision-conf.h
>> +++ b/sysdeps/unix/sysv/linux/s390/elision-conf.h
>> @@ -15,7 +15,6 @@
>>     You should have received a copy of the GNU Lesser General Public
>>     License along with the GNU C Library; if not, see
>>     <http://www.gnu.org/licenses/>.  */
>> -#ifdef ENABLE_LOCK_ELISION
>>  #ifndef _ELISION_CONF_H
>>  #define _ELISION_CONF_H 1
>>
>> @@ -41,4 +40,3 @@ extern int __pthread_force_elision attribute_hidden;
>>  #define HAVE_ELISION 1
>>
>>  #endif
>> -#endif
>> diff --git a/sysdeps/unix/sysv/linux/s390/force-elision.h 
>> b/sysdeps/unix/sysv/linux/s390/force-elision.h
>> index 3ae3bcd..8e1e33e 100644
>> --- a/sysdeps/unix/sysv/linux/s390/force-elision.h
>> +++ b/sysdeps/unix/sysv/linux/s390/force-elision.h
>> @@ -16,7 +16,6 @@
>>     License along with the GNU C Library; if not, see
>>     <http://www.gnu.org/licenses/>.  */
>>
>> -#ifdef ENABLE_LOCK_ELISION
>>  /* Automatically enable elision for existing user lock kinds.  */
>>  #define FORCE_ELISION(m, s)                        \
>>    if (__pthread_force_elision                        \
>> @@ -25,4 +24,3 @@
>>        mutex->__data.__kind |= PTHREAD_MUTEX_ELISION_NP;            \
>>        s;                                \
>>      }
>> -#endif
>> diff --git a/sysdeps/unix/sysv/linux/s390/lowlevellock.h 
>> b/sysdeps/unix/sysv/linux/s390/lowlevellock.h
>> index 604137f..48f87a8 100644
>> --- a/sysdeps/unix/sysv/linux/s390/lowlevellock.h
>> +++ b/sysdeps/unix/sysv/linux/s390/lowlevellock.h
>> @@ -22,7 +22,6 @@
>>  #include <sysdeps/nptl/lowlevellock.h>
>>
>>  /* Transactional lock elision definitions.  */
>> -# ifdef ENABLE_LOCK_ELISION
>>  extern int __lll_timedlock_elision
>>    (int *futex, short *adapt_count, const struct timespec *timeout, 
>> int private)
>>    attribute_hidden;
>> @@ -45,6 +44,5 @@ extern int __lll_trylock_elision(int *futex, short 
>> *adapt_count)
>>    __lll_unlock_elision (&(futex), &(adapt_count), private)
>>  #  define lll_trylock_elision(futex, adapt_count) \
> Can you adjust the occurences of "#  define" within the old #ifdef 
> ENABLE_LOCK_ELISON block to "# define".
> 
>>    __lll_trylock_elision(&(futex), &(adapt_count))
>> -# endif  /* ENABLE_LOCK_ELISION */
>>
>>  #endif    /* lowlevellock.h */
>> diff --git a/sysdeps/unix/sysv/linux/x86/elision-conf.c 
>> b/sysdeps/unix/sysv/linux/x86/elision-conf.c
>> index 673b000..7d3d8fd 100644
>> --- a/sysdeps/unix/sysv/linux/x86/elision-conf.c
>> +++ b/sysdeps/unix/sysv/linux/x86/elision-conf.c
>> @@ -21,6 +21,7 @@
>>  #include <init-arch.h>
>>  #include <elision-conf.h>
>>  #include <unistd.h>
>> +#include <elf/dl-tunables.h>
>>
>>  /* Reasonable initial tuning values, may be revised in the future.
>>     This is a conservative initial value.  */
>> @@ -52,17 +53,46 @@ int __pthread_force_elision attribute_hidden;
>>
>>  /* Initialize elison.  */
>>
>> +static inline void
>> +do_set_elision_enable (bool elision_enable)
>> +{
>> +  /* If elision is not enabled, or we are in a secure mode,
>> +     make sure elision is never used...  */
>> +  if (!elision_enable || __libc_enable_secure)
>> +    {
>> +      __pthread_force_elision = 0;
>> +      return;
>> +    }
>> +
>> +  /* ... otherwise enable elision based on hardare availability.  */
>> +  __pthread_force_elision = HAS_CPU_FEATURE (RTM);
>> +}
>> +
>> +#if HAVE_TUNABLES
>> +/* The elision->enable tunable is either 0 or 1 to indicate that
>> +   elision should be disabled or enabled respectively.  Availability at
>> +   the hardware level will still dictate if the feature is used.  */
>> +void
>> +DL_TUNABLE_CALLBACK (set_elision_enable) (tunable_val_t *valp)
>> +{
>> +  int32_t elision_enable = (int32_t) valp->numval;
>> +  do_set_elision_enable (elision_enable ? true : false);
>> +}
>> +#endif
>> +
>>  static void
>>  elision_init (int argc __attribute__ ((unused)),
>>            char **argv  __attribute__ ((unused)),
>>            char **environ)
>>  {
>> -  int elision_available = HAS_CPU_FEATURE (RTM);
>> -#ifdef ENABLE_LOCK_ELISION
>> -  __pthread_force_elision = __libc_enable_secure ? 0 : 
>> elision_available;
>> +#if HAVE_TUNABLES
>> +  /* Elision depends on tunables to enable and tune elision at 
>> runtime.  */
>> +# define TUNABLE_NAMESPACE elision
>> +  TUNABLE_SET_VAL_WITH_CALLBACK (enable, NULL, set_elision_enable);
>> +#else
>> +  /* Disable elision when built without tunables.  */
>> +  do_set_elision_enable (false);
>>  #endif
>> -  if (!elision_available)
>> -    __elision_aconf.retry_try_xbegin = 0; /* Disable elision on 
>> rwlocks */
>>  }
>>
>>  #ifdef SHARED
>> ---
>>
>

Patch

diff --git a/sysdeps/s390/configure.ac b/sysdeps/s390/configure.ac
index 8a782e7..62bcfb9 100644
--- a/sysdeps/s390/configure.ac
+++ b/sysdeps/s390/configure.ac
@@ -32,7 +32,7 @@  else
  fi
  rm -f conftest* ])

-if test "$enable_lock_elision" = yes && test 
"$libc_cv_gcc_builtin_tbegin" = no ; then
+if test "$libc_cv_gcc_builtin_tbegin" = no ; then
     critic_missing="$critic_missing The used GCC has no support for 
__builtin_tbegin, which is needed for lock-elision on target S390."
  fi

Note: __builtin_tbegin is available on RHEL/SLES GCC 4.8.5.


Please remove '--enable-lock-elision=yes' in INSTALL, too.

With these mentioned changes and the comments below,
I could build glibc and the testsuite runs without regressions.

I've also used a small s390 specific test program to check wether a 
mutex was elided or not:
./prog
Lock was a normal lock!

GLIBC_TUNABLES=glibc.elision.enable=0 ./prog
Lock was a normal lock!

GLIBC_TUNABLES=glibc.elision.enable=1 ./prog
Lock was elided via a transaction! (nesting-depth=1)

GLIBC_TUNABLES=glibc.elision.enable=1 ./prog_secure
Lock was a normal lock!

GLIBC_TUNABLES=glibc.elision.enable=2 ./prog
Lock was a normal lock!

GLIBC_TUNABLES=glibc.elision.enable=yes ./prog
Lock was a normal lock!


> Thoughts?
>
> diff --git a/config.h.in b/config.h.in
> index 2caa412..47b139e 100644
> --- a/config.h.in
> +++ b/config.h.in
> @@ -147,9 +147,6 @@
>  /* Define if __stack_chk_guard canary should be randomized at program startup.  */
>  #undef ENABLE_STACKGUARD_RANDOMIZE
>
> -/* Define if lock elision should be enabled by default.  */
> -#undef ENABLE_LOCK_ELISION
> -
>  /* Package description.  */
>  #undef PKGVERSION
>
> diff --git a/configure b/configure
> index 422482f..d3b68c1 100755
> --- a/configure
> +++ b/configure
> @@ -677,7 +677,6 @@ enable_werror
>  all_warnings
>  force_install
>  bindnow
> -enable_lock_elision
>  hardcoded_path_in_tests
>  enable_timezone_tools
>  use_default_link
> @@ -766,7 +765,6 @@ enable_profile
>  enable_timezone_tools
>  enable_hardcoded_path_in_tests
>  enable_stackguard_randomization
> -enable_lock_elision
>  enable_add_ons
>  enable_hidden_plt
>  enable_bind_now
> @@ -1427,8 +1425,6 @@ Optional Features:
>    --enable-stackguard-randomization
>                            initialize __stack_chk_guard canary with a random
>                            number at program start
> -  --enable-lock-elision=yes/no
> -                          Enable lock elision for pthread mutexes by default
>    --enable-add-ons[=DIRS...]
>                            configure and build add-ons in DIR1,DIR2,... search
>                            for add-ons if no parameter given
> @@ -3395,19 +3391,6 @@ if test "$enable_stackguard_randomize" = yes; then
>
>  fi
>
> -# Check whether --enable-lock-elision was given.
> -if test "${enable_lock_elision+set}" = set; then :
> -  enableval=$enable_lock_elision; enable_lock_elision=$enableval
> -else
> -  enable_lock_elision=no
> -fi
> -
> -
> -if test "$enable_lock_elision" = yes ; then
> -  $as_echo "#define ENABLE_LOCK_ELISION 1" >>confdefs.h
> -
> -fi
> -
>  # Check whether --enable-add-ons was given.
>  if test "${enable_add_ons+set}" = set; then :
>    enableval=$enable_add_ons;
> diff --git a/configure.ac b/configure.ac
> index 7f43042..a970296 100644
> --- a/configure.ac
> +++ b/configure.ac
> @@ -199,16 +199,6 @@ if test "$enable_stackguard_randomize" = yes; then
>    AC_DEFINE(ENABLE_STACKGUARD_RANDOMIZE)
>  fi
>
> -AC_ARG_ENABLE([lock-elision],
> -	      AC_HELP_STRING([--enable-lock-elision[=yes/no]],
> -			     [Enable lock elision for pthread mutexes by default]),
> -	      [enable_lock_elision=$enableval],
> -	      [enable_lock_elision=no])
> -AC_SUBST(enable_lock_elision)
> -if test "$enable_lock_elision" = yes ; then
> -  AC_DEFINE(ENABLE_LOCK_ELISION)
> -fi
> -
>  dnl Generic infrastructure for drop-in additions to libc.
>  AC_ARG_ENABLE([add-ons],
>  	      AC_HELP_STRING([--enable-add-ons@<:@=DIRS...@:>@],
> diff --git a/elf/dl-tunables.h b/elf/dl-tunables.h
> index f33adfb..3dad518 100644
> --- a/elf/dl-tunables.h
> +++ b/elf/dl-tunables.h
> @@ -18,8 +18,8 @@
>     License along with the GNU C Library; if not, see
>     <http://www.gnu.org/licenses/>.  */
>
> -#ifndef _TUNABLES_H_
> -#define _TUNABLES_H_
> +#ifndef _DL_TUNABLES_H_
> +#define _DL_TUNABLES_H_
>
>  #if !HAVE_TUNABLES
>  static inline void
> diff --git a/elf/dl-tunables.list b/elf/dl-tunables.list
> index b9f1488..97062f9 100644
> --- a/elf/dl-tunables.list
> +++ b/elf/dl-tunables.list
> @@ -77,4 +77,12 @@ glibc {
>        security_level: SXID_IGNORE
>      }
>    }
> +  elision {
> +    enable {
> +      type: INT_32
> +      minval: 0
> +      maxval: 1
> +      security_level: SXID_IGNORE
> +    }
> +  }
>  }
> diff --git a/nptl/Makefile b/nptl/Makefile
> index 6d48c0c..a720612 100644
> --- a/nptl/Makefile
> +++ b/nptl/Makefile
> @@ -704,6 +704,10 @@ $(objpfx)tst-oddstacklimit.out: $(objpfx)tst-oddstacklimit $(objpfx)tst-basic1
>  	$(evaluate-test)
>  endif
>
> +# Disable elision for tst-mutex8 so it can verify error case for
> +# destroying a mutex.
> +tst-mutex8-ENV = GLIBC_TUNABLES=glibc.elision.enable=0
> +
>  # The tests here better do not run in parallel
>  ifneq ($(filter %tests,$(MAKECMDGOALS)),)
>  .NOTPARALLEL:
> diff --git a/nptl/tst-mutex8.c b/nptl/tst-mutex8.c
> index 1d288d2..ef59db5 100644
> --- a/nptl/tst-mutex8.c
> +++ b/nptl/tst-mutex8.c
> @@ -127,9 +127,8 @@ check_type (const char *mas, pthread_mutexattr_t *ma)
>        return 1;
>      }
>
> -  /* Elided mutexes don't fail destroy. If elision is not explicitly disabled
> -     we don't know, so can also not check this.  */
> -#ifndef ENABLE_LOCK_ELISION
> +  /* Elided mutexes don't fail destroy, but this test is run with
> +     elision disabled so we can test them.  */
>    e = pthread_mutex_destroy (m);
>    if (e == 0)
>      {
> @@ -142,7 +141,6 @@ check_type (const char *mas, pthread_mutexattr_t *ma)
>  	      mas);
>        return 1;
>      }
> -#endif
>
>    if (pthread_mutex_unlock (m) != 0)
>      {
> @@ -157,7 +155,6 @@ check_type (const char *mas, pthread_mutexattr_t *ma)
>      }
>
>    /* Elided mutexes don't fail destroy.  */
> -#ifndef ENABLE_LOCK_ELISION
>    e = pthread_mutex_destroy (m);
>    if (e == 0)
>      {
> @@ -171,7 +168,6 @@ mutex_destroy of self-trylocked mutex did not return EBUSY %s\n",
>  	      mas);
>        return 1;
>      }
> -#endif
>
>    if (pthread_mutex_unlock (m) != 0)
>      {
> @@ -207,7 +203,6 @@ mutex_destroy of self-trylocked mutex did not return EBUSY %s\n",
>      }
>
>    /* Elided mutexes don't fail destroy.  */
> -#ifndef ENABLE_LOCK_ELISION
>    e = pthread_mutex_destroy (m);
>    if (e == 0)
>      {
> @@ -220,7 +215,6 @@ mutex_destroy of self-trylocked mutex did not return EBUSY %s\n",
>  mutex_destroy of condvar-used mutex did not return EBUSY for %s\n", mas);
>        return 1;
>      }
> -#endif
>
>    done = true;
>    if (pthread_cond_signal (&c) != 0)
> @@ -280,7 +274,6 @@ mutex_destroy of condvar-used mutex did not return EBUSY for %s\n", mas);
>      }
>
>    /* Elided mutexes don't fail destroy.  */
> -#ifndef ENABLE_LOCK_ELISION
>    e = pthread_mutex_destroy (m);
>    if (e == 0)
>      {
> @@ -295,7 +288,6 @@ mutex_destroy of condvar-used mutex did not return EBUSY for %s\n", mas);
>  	      mas);
>        return 1;
>      }
> -#endif
>
>    if (pthread_cancel (th) != 0)
>      {
> diff --git a/scripts/gen-tunables.awk b/scripts/gen-tunables.awk
> index 601240a..6dba7e1 100644
> --- a/scripts/gen-tunables.awk
> +++ b/scripts/gen-tunables.awk
> @@ -122,9 +122,9 @@ END {
>    }
>
>    print "/* AUTOGENERATED by gen-tunables.awk.  */"
> -  print "#ifndef _TUNABLES_H_"
> +  print "#ifndef _DL_TUNABLES_H_"
>    print "# error \"Do not include this file directly.\""
> -  print "# error \"Include tunables.h instead.\""
> +  print "# error \"Include dl-tunables.h instead.\""
>    print "#endif"
>
>    # Now, the enum names
> diff --git a/sysdeps/powerpc/nptl/elide.h b/sysdeps/powerpc/nptl/elide.h
> index 1c42814..06986cc 100644
> --- a/sysdeps/powerpc/nptl/elide.h
> +++ b/sysdeps/powerpc/nptl/elide.h
> @@ -19,7 +19,6 @@
>  #ifndef ELIDE_PPC_H
>  # define ELIDE_PPC_H
>
> -#ifdef ENABLE_LOCK_ELISION
>  # include <htm.h>
>  # include <elision-conf.h>
>
> @@ -114,12 +113,4 @@ __elide_unlock (int is_lock_free)
>  # define ELIDE_UNLOCK(is_lock_free) \
>    __elide_unlock (is_lock_free)
>
> -# else
> -
> -# define ELIDE_LOCK(adapt_count, is_lock_free) 0
> -# define ELIDE_TRYLOCK(adapt_count, is_lock_free, write) 0
> -# define ELIDE_UNLOCK(is_lock_free) 0
> -
> -#endif /* ENABLE_LOCK_ELISION  */
> -
>  #endif
> diff --git a/sysdeps/powerpc/powerpc32/sysdep.h b/sysdeps/powerpc/powerpc32/sysdep.h
> index f92ab2c..0ed83d3 100644
> --- a/sysdeps/powerpc/powerpc32/sysdep.h
> +++ b/sysdeps/powerpc/powerpc32/sysdep.h
> @@ -88,7 +88,7 @@ GOT_LABEL:			;					      \
>    cfi_endproc;								      \
>    ASM_SIZE_DIRECTIVE(name)
>
> -#if ! IS_IN(rtld) && defined (ENABLE_LOCK_ELISION)
> +#if ! IS_IN(rtld)
>  # define ABORT_TRANSACTION \
>      cmpwi    2,0;		\
>      beq      1f;		\
> diff --git a/sysdeps/powerpc/powerpc64/sysdep.h b/sysdeps/powerpc/powerpc64/sysdep.h
> index db7c1d7..79a2697 100644
> --- a/sysdeps/powerpc/powerpc64/sysdep.h
> +++ b/sysdeps/powerpc/powerpc64/sysdep.h
> @@ -272,7 +272,7 @@ LT_LABELSUFFIX(name,_name_end): ; \
>    TRACEBACK_MASK(name,mask)	\
>    END_2(name)
>
> -#if !IS_IN(rtld) && defined (ENABLE_LOCK_ELISION)
> +#if !IS_IN(rtld)
>  # define ABORT_TRANSACTION \
>      cmpdi    13,0;		\
>      beq      1f;		\
> diff --git a/sysdeps/powerpc/sysdep.h b/sysdeps/powerpc/sysdep.h
> index f07b959..d1a9bd9 100644
> --- a/sysdeps/powerpc/sysdep.h
> +++ b/sysdeps/powerpc/sysdep.h
> @@ -21,10 +21,8 @@
>   */
>  #define _SYSDEPS_SYSDEP_H 1
>  #include <bits/hwcap.h>
> -#ifdef ENABLE_LOCK_ELISION
>  #include <tls.h>
>  #include <htm.h>
> -#endif
>
>  #define PPC_FEATURE_970 (PPC_FEATURE_POWER4 + PPC_FEATURE_HAS_ALTIVEC)
>
> @@ -176,7 +174,7 @@
>     we abort transaction just before syscalls.
>
>     [1] Documentation/powerpc/transactional_memory.txt [Syscalls]  */
> -#if !IS_IN(rtld) && defined (ENABLE_LOCK_ELISION)
> +#if !IS_IN(rtld)
>  # define ABORT_TRANSACTION \
>    ({ 						\
>      if (THREAD_GET_TM_CAPABLE ())		\
> diff --git a/sysdeps/s390/nptl/bits/pthreadtypes.h b/sysdeps/s390/nptl/bits/pthreadtypes.h
> index 48ffdb4..88d21f0 100644
> --- a/sysdeps/s390/nptl/bits/pthreadtypes.h
> +++ b/sysdeps/s390/nptl/bits/pthreadtypes.h
> @@ -89,37 +89,25 @@ typedef union
>         binary compatibility with static initializers.  */
>      int __kind;
>  #if __WORDSIZE == 64
> -# ifdef ENABLE_LOCK_ELISION
>      short __spins;
>      short __elision;
>      /* Mutex __spins initializer used by PTHREAD_MUTEX_INITIALIZER.  */
> -#  define __PTHREAD_SPINS               0, 0
> -# else
> -    int __spins;
> -    /* Mutex __spins initializer used by PTHREAD_MUTEX_INITIALIZER.  */
> -#  define __PTHREAD_SPINS               0
> -# endif
> +# define __PTHREAD_SPINS               0, 0
>      __pthread_list_t __list;
>  # define __PTHREAD_MUTEX_HAVE_PREV	1
>  #else
>      unsigned int __nusers;
>      __extension__ union
>      {
> -# ifdef ENABLE_LOCK_ELISION
>        struct
>        {
>  	short __espins;
>  	short __elision;
>        } _d;
> -#  define __spins _d.__espins
> -#  define __elision _d.__elision
> -    /* Mutex __spins initializer used by PTHREAD_MUTEX_INITIALIZER.  */
> -#  define __PTHREAD_SPINS               { 0, 0 }
> -# else
> -      int __spins;
> -    /* Mutex __spins initializer used by PTHREAD_MUTEX_INITIALIZER.  */
> -#  define __PTHREAD_SPINS               0
> -# endif
> +# define __spins _d.__espins
> +# define __elision _d.__elision
> +      /* Mutex __spins initializer used by PTHREAD_MUTEX_INITIALIZER.  */
> +# define __PTHREAD_SPINS               { 0, 0 }
>        __pthread_slist_t __list;
>      };
>  #endif
Adhemerval's commit "Move shared pthread definitions to common headers"
consolidates the pthradtypes.h files.
Thus sysdeps/s390/nptl/bits/pthreadtypes.h does not exist anymore.
I've adjusted sysdeps/s390/nptl/bits/pthreadtypes-arch.h for my test:
diff --git a/sysdeps/s390/nptl/bits/pthreadtypes-arch.h 
b/sysdeps/s390/nptl/bits/pthreadtypes-arch.h
index 3a9ac57..db7195a 100644
--- a/sysdeps/s390/nptl/bits/pthreadtypes-arch.h
+++ b/sysdeps/s390/nptl/bits/pthreadtypes-arch.h
@@ -40,11 +40,7 @@ 
  /* Definitions for internal mutex struct.  */
  #define __PTHREAD_COMPAT_PADDING_MID
  #define __PTHREAD_COMPAT_PADDING_END
-#ifdef ENABLE_LOCK_ELISION
  #define __PTHREAD_MUTEX_LOCK_ELISION    1
-#else
-#define __PTHREAD_MUTEX_LOCK_ELISION	0
-#endif

  #define __LOCK_ALIGNMENT
  #define __ONCE_ALIGNMENT