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[RFC] tunables: Add elision tunable

Message ID 83765281-100b-a041-405e-d36b97581095@linux.vnet.ibm.com
State Superseded
Headers show

Commit Message

rcardoso@linux.vnet.ibm.com Sept. 11, 2017, 1:25 p.m. UTC
Hello,

Attached to this mail I have a patch which add elision to tunables 
framework. This is a rebase of Paul Murphy's patch [1]. Also there's a 
RFC related to this [2].

[1] https://patchwork.sourceware.org/patch/10342/
[2] https://patchwork.sourceware.org/patch/20407/
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Patch

From eb98c17fb08e7e5810af2108e820924cebf062d0 Mon Sep 17 00:00:00 2001
From: Rogerio Alves <rcardoso@linux.vnet.ibm.com>
Date: Thu, 6 Jul 2017 13:21:08 -0500
Subject: [PATCH v6] Add elision tunables.

This patch adds several new tunables to control the behavior of
elision on supported platforms.  This also disables elision
by default on powerpc.

This patch was initially proposed by Paul Murphy[1] but was
"staled" because the framework have changed since the patch was
originally proposed.

[1] https://patchwork.sourceware.org/patch/10342/

2017-06-06  Rogerio A. Cardoso  <rcardoso@linux.vnet.ibm.com>,
	    Paul E. Murphy  <murphyp@linux.vnet.ibm.com>

	* elf/dl-tunables.list: Add elision parameters.
	* manual/tunables.texi: Add entries about elision tunable.
	* sysdeps/unix/sysv/linux/powerpc/elision-conf.c:
	Add callback functions to dynamically enable/disable elision.
	Add multiple callbacks functions to set elision parameters.
	* sysdeps/unix/sysv/linux/s390/elision-conf.c: Likewise.
	* sysdeps/unix/sysv/linux/x86/elision-conf.c: Likewise.
---
 Changes in v6: Based on Gabriel review. Fix small issues. Add
set_elision on CALLBACK macro for x86 s390.

 Changes in v5: Based on Gabriel review. Fix things that was uncompliant with 
 code standards. Fix others small things on manual that I was forgot on the 
 last review. 

 Changes in v4: Based on Gabriel review. Fix some small things on manual.

 Changes in v3: Based on Tulio review. Changed namespace from pthread to elision.
 Fix lots of extra spaces and typos. Fix some space/tab issues. Running 
 checkpath script to catch some code format issues. Reworked on commit message. 

 Changes in v2: Based on Raji review. Created manual entry for elision tunables. 
 Fix extra spaces on tunables list. Fix incorrect macro parameter on elision 
 enable for s390. Fix identation on defines. Include missing tunable namespace 
 on x86/elision-conf.c. Using #ifdef instead #if

 elf/dl-tunables.list                           | 34 ++++++++++++
 manual/tunables.texi                           | 64 +++++++++++++++++++++++
 sysdeps/unix/sysv/linux/powerpc/elision-conf.c | 72 +++++++++++++++++++++++---
 sysdeps/unix/sysv/linux/s390/elision-conf.c    | 69 ++++++++++++++++++++++--
 sysdeps/unix/sysv/linux/x86/elision-conf.c     | 71 ++++++++++++++++++++++---
 5 files changed, 293 insertions(+), 17 deletions(-)

diff --git a/elf/dl-tunables.list b/elf/dl-tunables.list
index c188c6a..77dfcb4 100644
--- a/elf/dl-tunables.list
+++ b/elf/dl-tunables.list
@@ -96,4 +96,38 @@  glibc {
       default: HWCAP_IMPORTANT
       }
   }
+
+  elision {
+    enable {
+      type: INT_32
+      minval: 0
+      maxval: 1
+      security_level: SXID_IGNORE
+    }
+    skip_lock_busy {
+      type: INT_32
+      default: 3
+      security_level: SXID_IGNORE
+    }
+    skip_lock_internal_abort {
+      type: INT_32
+      default: 3
+      security_level: SXID_IGNORE
+    }
+    skip_lock_after_retries {
+      type: INT_32
+      default: 3
+      security_level: SXID_IGNORE
+    }
+    tries {
+      type: INT_32
+      default: 3
+      security_level: SXID_IGNORE
+    }
+    skip_trylock_internal_abort {
+      type: INT_32
+      default: 3
+      security_level: SXID_IGNORE
+    }
+  }
 }
diff --git a/manual/tunables.texi b/manual/tunables.texi
index 3c19567..5b73f73 100644
--- a/manual/tunables.texi
+++ b/manual/tunables.texi
@@ -31,6 +31,7 @@  their own namespace.
 @menu
 * Tunable names::  The structure of a tunable name
 * Memory Allocation Tunables::  Tunables in the memory allocation subsystem
+* Elision Tunables::  Tunables in elision subsystem
 * Hardware Capability Tunables::  Tunables that modify the hardware
 				  capabilities seen by @theglibc{}
 @end menu
@@ -224,6 +225,69 @@  bounded, the user may set this tunable to limit the number of chunks
 that are scanned from the unsorted list while searching for chunks to
 pre-fill the per-thread cache with.  The default, or when set to zero,
 is no limit.
+
+@node Elision Tunables
+@section Elision Tunables
+@cindex elision tunables
+@cindex tunables, elision
+
+@deftp {Tunable namespace} glibc.elision
+Elision behavior can be modified by setting any of the following tunables in
+the @code{elision} namespace:
+@end deftp
+
+@deftp Tunable glibc.elision.enable
+The @code{glibc.elision.enable} tunable enables lock elision if the feature is
+supported by the hardware.  If elision is not supported by the hardware this
+tunable has no effect.
+
+Elision tunables are supported for x86-64, PowerPC, and S390 architectures.
+@end deftp
+
+@deftp Tunable glibc.elision.skip_lock_busy
+The @code{glibc.elision.skip_lock_busy} tunable sets how many times to use a
+non-transactional lock after a transactional failure has occurred because the
+lock is already acquired.  Expressed in number of lock acquisition attempts.
+
+The default value of this tunable is @samp{3}.
+@end deftp
+
+@deftp Tunable glibc.elision.skip_lock_internal_abort
+The @code{glibc.elision.skip_lock_internal_abort} tunable sets how many times
+to not attempt to use elision if a transaction aborted due to reasons other
+than other threads' memory accesses.  Expressed in number of lock acquisition
+attempts.
+
+The default value of this tunable is @samp{3}.
+@end deftp
+
+@deftp Tunable glibc.elision.skip_lock_after_retries
+The @code{glibc.elision.skip_lock_after_retries} tunable sets how my times to
+try to elide a lock with transactions that only fail due other threads' memory
+accesses, before falling back to regular lock.
+Expressed in number of lock elision attempts.
+
+This tunable is not supported by x86.
+
+The default value of this tunable is @samp{3}.
+@end deftp
+
+@deftp Tunable glibc.elision.tries
+The @code{glibc.elision.tries} sets how many times we retry using elision if
+there is chance for the transaction to finish execution (e.g., it wasn't aborted
+due to the lock being already acquired).  This tunable is set to @samp{0} if
+elision is not supported by the hardware to avoid retries.
+
+The default value of this tunable is @samp{3}.
+@end deftp
+
+@deftp Tunable glibc.elision.skip_trylock_internal_abort
+The @code{glibc.elision.skip_trylock_internal_abort} tunable sets how many times
+to not attempt to use elision for trylocks if a transaction aborted due to
+reasons other than other threads' memory accesses.  Expressed in number of try
+lock attempts.
+
+The default value of this tunable is @samp{3}.
 @end deftp
 
 @node Hardware Capability Tunables
diff --git a/sysdeps/unix/sysv/linux/powerpc/elision-conf.c b/sysdeps/unix/sysv/linux/powerpc/elision-conf.c
index f631f0a..07ebe37 100644
--- a/sysdeps/unix/sysv/linux/powerpc/elision-conf.c
+++ b/sysdeps/unix/sysv/linux/powerpc/elision-conf.c
@@ -21,6 +21,10 @@ 
 #include <elision-conf.h>
 #include <unistd.h>
 #include <dl-procinfo.h>
+#ifdef HAVE_TUNABLES
+# include <elf/dl-tunables.h>
+# define TUNABLE_NAMESPACE elision
+#endif
 
 /* Reasonable initial tuning values, may be revised in the future.
    This is a conservative initial value.  */
@@ -50,7 +54,50 @@  struct elision_config __elision_aconf =
    DEFAULT locks should be automatically use elision in pthread_mutex_lock().
    Disabled for suid programs.  Only used when elision is available.  */
 
-int __pthread_force_elision attribute_hidden;
+int __pthread_force_elision attribute_hidden = 0;
+
+#ifdef HAVE_TUNABLES
+static inline void
+__always_inline
+do_set_elision_enable (int32_t elision_enable)
+{
+  /* Enable elision if it's avaliable in hardware.  */
+  if (elision_enable && !__libc_enable_secure)
+    __pthread_force_elision = (GLRO (dl_hwcap2)
+			       & PPC_FEATURE2_HAS_HTM) ? 1 : 0;
+}
+
+/* The pthread->elision_enable tunable is 0 or 1 indicating that elision
+   should be disabled or enabled respectively.  The feature will only be used
+   if it's supported by the hardware.  */
+
+void
+TUNABLE_CALLBACK (set_elision_enable) (tunable_val_t *valp)
+{
+  int32_t elision_enable = (int32_t) valp->numval;
+  do_set_elision_enable (elision_enable);
+}
+
+#define TUNABLE_CALLBACK_FNDECL(__name, __type)			\
+static inline void						\
+__always_inline							\
+do_set_elision_ ## __name (__type value)			\
+{								\
+  __elision_aconf.__name = value;				\
+}								\
+void								\
+TUNABLE_CALLBACK (set_elision_ ## __name) (tunable_val_t *valp) \
+{								\
+  __type value = (__type) (valp)->numval;			\
+  do_set_elision_ ## __name (value);				\
+}
+
+TUNABLE_CALLBACK_FNDECL (skip_lock_busy, int32_t);
+TUNABLE_CALLBACK_FNDECL (skip_lock_internal_abort, int32_t);
+TUNABLE_CALLBACK_FNDECL (skip_lock_out_of_tbegin_retries, int32_t);
+TUNABLE_CALLBACK_FNDECL (try_tbegin, int32_t);
+TUNABLE_CALLBACK_FNDECL (skip_trylock_internal_abort, int32_t);
+#endif
 
 /* Initialize elision.  */
 
@@ -59,13 +106,26 @@  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;
+#ifdef HAVE_TUNABLES
+  /* Elision depends on tunables and must be explicitly turned on by setting
+     the appropriate tunable on a supported platform.  */
+
+  TUNABLE_GET (enable, int32_t,
+	       TUNABLE_CALLBACK (set_elision_enable));
+  TUNABLE_GET (skip_lock_busy, int32_t,
+	       TUNABLE_CALLBACK (set_elision_skip_lock_busy));
+  TUNABLE_GET (skip_lock_internal_abort, int32_t,
+	       TUNABLE_CALLBACK (set_elision_skip_lock_internal_abort));
+  TUNABLE_GET (skip_lock_after_retries, int32_t,
+	       TUNABLE_CALLBACK (set_elision_skip_lock_out_of_tbegin_retries));
+  TUNABLE_GET (tries, int32_t,
+	       TUNABLE_CALLBACK (set_elision_try_tbegin));
+  TUNABLE_GET (skip_trylock_internal_abort, int32_t,
+	       TUNABLE_CALLBACK (set_elision_skip_trylock_internal_abort));
 #endif
+
   if (!__pthread_force_elision)
-    /* Disable elision on rwlocks.  */
-    __elision_aconf.try_tbegin = 0;
+    __elision_aconf.try_tbegin = 0; /* Disable elision on rwlocks.  */
 }
 
 #ifdef SHARED
diff --git a/sysdeps/unix/sysv/linux/s390/elision-conf.c b/sysdeps/unix/sysv/linux/s390/elision-conf.c
index cc0fdef..5f9c6d1 100644
--- a/sysdeps/unix/sysv/linux/s390/elision-conf.c
+++ b/sysdeps/unix/sysv/linux/s390/elision-conf.c
@@ -21,6 +21,10 @@ 
 #include <elision-conf.h>
 #include <unistd.h>
 #include <dl-procinfo.h>
+#ifdef HAVE_TUNABLES
+# include <elf/dl-tunables.h>
+# define TUNABLE_NAMESPACE elision
+#endif
 
 /* Reasonable initial tuning values, may be revised in the future.
    This is a conservative initial value.  */
@@ -53,6 +57,48 @@  struct elision_config __elision_aconf =
 
 int __pthread_force_elision attribute_hidden = 0;
 
+#ifdef HAVE_TUNABLES
+static inline void
+__always_inline
+do_set_elision_enable (int32_t elision_enable)
+{
+  /* Enable elision if it's avaliable in hardware.  */
+  if (elision_enable && !__libc_enable_secure)
+    __pthread_force_elision = (GLRO (dl_hwcap) & HWCAP_S390_TE) ? 1 : 0;
+}
+
+/* The pthread->elision_enable tunable is 0 or 1 indicating that elision
+   should be disabled or enabled respectively.  The feature will only be used
+   if it's supported by the hardware.  */
+
+void
+TUNABLE_CALLBACK (set_elision_enable) (tunable_val_t *valp)
+{
+  int32_t elision_enable = (int32_t) valp->numval;
+  do_set_elision_enable (elision_enable);
+}
+
+#define TUNABLE_CALLBACK_FNDECL(__name, __type)			\
+static inline void						\
+__always_inline							\
+do_set_elision_ ## __name (__type value)			\
+{								\
+  __elision_aconf.__name = value;				\
+}								\
+void								\
+TUNABLE_CALLBACK (set_elision_ ## __name) (tunable_val_t *valp) \
+{								\
+  __type value = (__type) (valp)->numval;			\
+  do_set_elision_ ## __name (value);				\
+}
+
+TUNABLE_CALLBACK_FNDECL (skip_lock_busy, int32_t);
+TUNABLE_CALLBACK_FNDECL (skip_lock_internal_abort, int32_t);
+TUNABLE_CALLBACK_FNDECL (skip_lock_out_of_tbegin_retries, int32_t);
+TUNABLE_CALLBACK_FNDECL (try_tbegin, int32_t);
+TUNABLE_CALLBACK_FNDECL (skip_trylock_internal_abort, int32_t);
+#endif
+
 /* Initialize elison.  */
 
 static void
@@ -60,11 +106,26 @@  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;
+#ifdef HAVE_TUNABLES
+  /* Elision depends on tunables and must be explicitly turned on by setting
+     the appropriate tunable on a supported platform.  */
+
+  TUNABLE_GET (enable, int32_t,
+	       TUNABLE_CALLBACK (set_elision_enable));
+  TUNABLE_GET (skip_lock_busy, int32_t,
+	       TUNABLE_CALLBACK (set_elision_skip_lock_busy));
+  TUNABLE_GET (skip_lock_internal_abort, int32_t,
+	       TUNABLE_CALLBACK (set_elision_skip_lock_internal_abort));
+  TUNABLE_GET (skip_lock_after_retries, int32_t,
+	       TUNABLE_CALLBACK (set_elision_skip_lock_out_of_tbegin_retries));
+  TUNABLE_GET (tries, int32_t,
+	       TUNABLE_CALLBACK (set_elision_try_tbegin));
+  TUNABLE_GET (skip_trylock_internal_abort, int32_t,
+	       TUNABLE_CALLBACK (set_elision_skip_trylock_internal_abort));
+#endif
 
-  __pthread_force_elision = __libc_enable_secure ? 0 : elision_available;
+  if (!__pthread_force_elision)
+    __elision_aconf.try_tbegin = 0; /* Disable elision on rwlocks.  */
 }
 
 #ifdef SHARED
diff --git a/sysdeps/unix/sysv/linux/x86/elision-conf.c b/sysdeps/unix/sysv/linux/x86/elision-conf.c
index 673b000..02e87dc 100644
--- a/sysdeps/unix/sysv/linux/x86/elision-conf.c
+++ b/sysdeps/unix/sysv/linux/x86/elision-conf.c
@@ -21,6 +21,10 @@ 
 #include <init-arch.h>
 #include <elision-conf.h>
 #include <unistd.h>
+#ifdef HAVE_TUNABLES
+# include <elf/dl-tunables.h>
+# define TUNABLE_NAMESPACE elision
+#endif
 
 /* Reasonable initial tuning values, may be revised in the future.
    This is a conservative initial value.  */
@@ -48,21 +52,74 @@  struct elision_config __elision_aconf =
    pthread_mutex_lock().  Disabled for suid programs.  Only used when elision
    is available.  */
 
-int __pthread_force_elision attribute_hidden;
+int __pthread_force_elision attribute_hidden = 0;
+
+#ifdef HAVE_TUNABLES
+static inline void
+__always_inline
+do_set_elision_enable (int32_t elision_enable)
+{
+  /* Enable elision if it's avaliable in hardware.  */
+  if (elision_enable && !__libc_enable_secure)
+    __pthread_force_elision = HAS_CPU_FEATURE (RTM) ? 1 : 0;
+}
+
+/* The pthread->elision_enable tunable is 0 or 1 indicating that elision
+   should be disabled or enabled respectively.  The feature will only be used
+   if it's supported by the hardware.  */
+
+void
+TUNABLE_CALLBACK (set_elision_enable) (tunable_val_t *valp)
+{
+  int32_t elision_enable = (int32_t) valp->numval;
+  do_set_elision_enable (elision_enable);
+}
+
+#define TUNABLE_CALLBACK_FNDECL(__name, __type)			\
+static inline void						\
+__always_inline							\
+do_set_elision_ ## __name (__type value)			\
+{								\
+  __elision_aconf.__name = value;				\
+}								\
+void								\
+TUNABLE_CALLBACK (set_elision_ ## __name) (tunable_val_t *valp) \
+{								\
+  __type value = (__type) (valp)->numval;			\
+  do_set_elision_ ## __name (value);				\
+}
 
-/* Initialize elison.  */
+TUNABLE_CALLBACK_FNDECL (skip_lock_busy, int32_t);
+TUNABLE_CALLBACK_FNDECL (skip_lock_internal_abort, int32_t);
+TUNABLE_CALLBACK_FNDECL (retry_try_xbegin, int32_t);
+TUNABLE_CALLBACK_FNDECL (skip_trylock_internal_abort, int32_t);
+#endif
+
+/* Initialize elision.  */
 
 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;
+#ifdef HAVE_TUNABLES
+  /* Elision depends on tunables and must be explicitly turned on by setting
+     the appropriate tunable on a supported platform.  */
+
+  TUNABLE_GET (enable, int32_t,
+	       TUNABLE_CALLBACK (set_elision_enable));
+  TUNABLE_GET (skip_lock_busy, int32_t,
+	       TUNABLE_CALLBACK (set_elision_skip_lock_busy));
+  TUNABLE_GET (skip_lock_internal_abort, int32_t,
+	       TUNABLE_CALLBACK (set_elision_skip_lock_internal_abort));
+  TUNABLE_GET (tries, int32_t,
+	       TUNABLE_CALLBACK (set_elision_retry_try_xbegin));
+  TUNABLE_GET (skip_trylock_internal_abort, int32_t,
+	       TUNABLE_CALLBACK (set_elision_skip_trylock_internal_abort));
 #endif
-  if (!elision_available)
-    __elision_aconf.retry_try_xbegin = 0; /* Disable elision on rwlocks */
+
+  if (!__pthread_force_elision)
+    __elision_aconf.retry_try_xbegin = 0; /* Disable elision on rwlocks.  */
 }
 
 #ifdef SHARED
-- 
2.7.4