[v1] sysdeps: Add 'get_fast_jitter' interace in fast-jitter.h

  'get_fast_jitter' is meant to be used purely for performance
purposes. In all cases it's used it should be acceptable to get no
randomness (see default case). An example use case is in setting
jitter for retries between threads at a lock. There is a
performance benefit to having jitter, but only if the jitter can
be generated very quickly and ultimately there is no serious issue
if no jitter is generated.

The implementation generally uses 'HP_TIMING_NOW' or another cycle
counter when the architecture supports it. The default case just
returns zero.
---
 sysdeps/aarch64/fast-jitter.h | 33 +++++++++++++++++++++++++++++++++
 sysdeps/alpha/fast-jitter.h   | 34 ++++++++++++++++++++++++++++++++++
 sysdeps/generic/fast-jitter.h | 35 +++++++++++++++++++++++++++++++++++
 sysdeps/s390/fast-jitter.h    | 33 +++++++++++++++++++++++++++++++++
 sysdeps/sparc/fast-jitter.h   | 33 +++++++++++++++++++++++++++++++++
 sysdeps/x86_64/fast-jitter.h  | 30 ++++++++++++++++++++++++++++++
 6 files changed, 198 insertions(+)
 create mode 100644 sysdeps/aarch64/fast-jitter.h
 create mode 100644 sysdeps/alpha/fast-jitter.h
 create mode 100644 sysdeps/generic/fast-jitter.h
 create mode 100644 sysdeps/s390/fast-jitter.h
 create mode 100644 sysdeps/sparc/fast-jitter.h
 create mode 100644 sysdeps/x86_64/fast-jitter.h
  

On Mon, Apr 4, 2022 at 4:39 PM Noah Goldstein <goldstein.w.n@gmail.com> wrote:
>
> 'get_fast_jitter' is meant to be used purely for performance
> purposes. In all cases it's used it should be acceptable to get no
> randomness (see default case). An example use case is in setting
> jitter for retries between threads at a lock. There is a
> performance benefit to having jitter, but only if the jitter can
> be generated very quickly and ultimately there is no serious issue
> if no jitter is generated.
>
> The implementation generally uses 'HP_TIMING_NOW' or another cycle
> counter when the architecture supports it. The default case just
> returns zero.
> ---
>  sysdeps/aarch64/fast-jitter.h | 33 +++++++++++++++++++++++++++++++++
>  sysdeps/alpha/fast-jitter.h   | 34 ++++++++++++++++++++++++++++++++++
>  sysdeps/generic/fast-jitter.h | 35 +++++++++++++++++++++++++++++++++++
>  sysdeps/s390/fast-jitter.h    | 33 +++++++++++++++++++++++++++++++++
>  sysdeps/sparc/fast-jitter.h   | 33 +++++++++++++++++++++++++++++++++
>  sysdeps/x86_64/fast-jitter.h  | 30 ++++++++++++++++++++++++++++++
>  6 files changed, 198 insertions(+)
>  create mode 100644 sysdeps/aarch64/fast-jitter.h
>  create mode 100644 sysdeps/alpha/fast-jitter.h
>  create mode 100644 sysdeps/generic/fast-jitter.h
>  create mode 100644 sysdeps/s390/fast-jitter.h
>  create mode 100644 sysdeps/sparc/fast-jitter.h
>  create mode 100644 sysdeps/x86_64/fast-jitter.h
>
> diff --git a/sysdeps/aarch64/fast-jitter.h b/sysdeps/aarch64/fast-jitter.h
> new file mode 100644
> index 0000000000..fb09d2632c
> --- /dev/null
> +++ b/sysdeps/aarch64/fast-jitter.h
> @@ -0,0 +1,33 @@
> +/* Fast jitter on arm with HP_TIMING_NOW
> +   Copyright (C) 2022-2022 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <https://www.gnu.org/licenses/>.  */
> +
> +#ifndef _FAST_JITTER_H
> +# define _FAST_JITTER_H
> +
> +#include <stdint.h>
> +#include <hp-timing.h>
> +
> +static inline uint32_t
> +get_fast_jitter (void)
> +{
> +  hp_timing_t jitter;
> +  HP_TIMING_NOW (jitter);
> +  return (uint32_t) jitter;
> +}
> +
> +#endif
> diff --git a/sysdeps/alpha/fast-jitter.h b/sysdeps/alpha/fast-jitter.h
> new file mode 100644
> index 0000000000..0a24290eaa
> --- /dev/null
> +++ b/sysdeps/alpha/fast-jitter.h
> @@ -0,0 +1,34 @@
> +/* Fast jitter on alpha with rpcc
> +   Copyright (C) 2022-2022 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <https://www.gnu.org/licenses/>.  */
> +
> +#ifndef _FAST_JITTER_H
> +# define _FAST_JITTER_H
> +
> +#include <stdint.h>
> +
> +static inline uint32_t
> +get_fast_jitter (void)
> +{
> +  unsigned long int x_;
> +  asm volatile ("rpcc %0" : "=r"(x_));
> +  /* Don't both with process offset.  We only need jitter not
> +     monotonic cycle count.  */
> +  return (uint32_t) x;
> +}
> +
> +#endif
> diff --git a/sysdeps/generic/fast-jitter.h b/sysdeps/generic/fast-jitter.h
> new file mode 100644
> index 0000000000..63bcf3ccd7
> --- /dev/null
> +++ b/sysdeps/generic/fast-jitter.h
> @@ -0,0 +1,35 @@
> +/* Fallback for fast jitter just return 0.
> +   Copyright (C) 2019-2022 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <https://www.gnu.org/licenses/>.  */
> +
> +#ifndef _FAST_JITTER_H
> +# define _FAST_JITTER_H
> +
> +#include <stdint.h>
> +
> +/* Baseline just return 0.  We could create jitter using a clock or
> +   'random_bits' but that may imply a syscall and the goal of
> +   'get_fast_jitter' is minimal overhead "randomness" when such
> +   randomness helps performance.  Adding high overhead the function
> +   defeats the purpose.  */
> +static inline uint32_t
> +get_fast_jitter (void)
> +{
> +  return 0;
> +}
> +
> +#endif
> diff --git a/sysdeps/s390/fast-jitter.h b/sysdeps/s390/fast-jitter.h
> new file mode 100644
> index 0000000000..eb905b1413
> --- /dev/null
> +++ b/sysdeps/s390/fast-jitter.h
> @@ -0,0 +1,33 @@
> +/* Fast jitter on s390 with HP_TIMING_NOW
> +   Copyright (C) 2022-2022 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <https://www.gnu.org/licenses/>.  */
> +
> +#ifndef _FAST_JITTER_H
> +# define _FAST_JITTER_H
> +
> +#include <stdint.h>
> +#include <hp-timing.h>
> +
> +static inline uint32_t
> +get_fast_jitter (void)
> +{
> +  hp_timing_t jitter;
> +  HP_TIMING_NOW (jitter);
> +  return (uint32_t) jitter;
> +}
> +
> +#endif
> diff --git a/sysdeps/sparc/fast-jitter.h b/sysdeps/sparc/fast-jitter.h
> new file mode 100644
> index 0000000000..f4413754c5
> --- /dev/null
> +++ b/sysdeps/sparc/fast-jitter.h
> @@ -0,0 +1,33 @@
> +/* Fast jitter on sparc with HP_TIMING_NOW
> +   Copyright (C) 2022-2022 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <https://www.gnu.org/licenses/>.  */
> +
> +#ifndef _FAST_JITTER_H
> +# define _FAST_JITTER_H
> +
> +#include <stdint.h>
> +#include <hp-timing.h>
> +
> +static inline uint32_t
> +get_fast_jitter (void)
> +{
> +  hp_timing_t jitter;
> +  HP_TIMING_NOW (jitter);
> +  return (uint32_t) jitter;
> +}
> +
> +#endif
> diff --git a/sysdeps/x86_64/fast-jitter.h b/sysdeps/x86_64/fast-jitter.h
> new file mode 100644
> index 0000000000..1140f1c295
> --- /dev/null
> +++ b/sysdeps/x86_64/fast-jitter.h
> @@ -0,0 +1,30 @@
> +/* X86 use rdtsc to quickly generate pseudo-random for jitter
> +   Copyright (C) 2022-2022 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <https://www.gnu.org/licenses/>.  */
> +
> +#ifndef _FAST_JITTER_H
> +# define _FAST_JITTER_H
> +
> +#include <stdint.h>
> +
> +static inline uint32_t
> +get_fast_jitter (void)
> +{
> +  return __builtin_ia32_rdtsc ();
> +}
> +
> +#endif
> --
> 2.25.1
>

Ping.
  

On 04/04/2022 18:39, Noah Goldstein via Libc-alpha wrote:
> 'get_fast_jitter' is meant to be used purely for performance
> purposes. In all cases it's used it should be acceptable to get no
> randomness (see default case). An example use case is in setting
> jitter for retries between threads at a lock. There is a
> performance benefit to having jitter, but only if the jitter can
> be generated very quickly and ultimately there is no serious issue
> if no jitter is generated.
> 
> The implementation generally uses 'HP_TIMING_NOW' or another cycle
> counter when the architecture supports it. The default case just
> returns zero.

I think it should ok, although I think it would be better to be sent
along with a actual usage (as the pthread mutex optimization).

> ---
>  sysdeps/aarch64/fast-jitter.h | 33 +++++++++++++++++++++++++++++++++
>  sysdeps/alpha/fast-jitter.h   | 34 ++++++++++++++++++++++++++++++++++
>  sysdeps/generic/fast-jitter.h | 35 +++++++++++++++++++++++++++++++++++
>  sysdeps/s390/fast-jitter.h    | 33 +++++++++++++++++++++++++++++++++
>  sysdeps/sparc/fast-jitter.h   | 33 +++++++++++++++++++++++++++++++++
>  sysdeps/x86_64/fast-jitter.h  | 30 ++++++++++++++++++++++++++++++
>  6 files changed, 198 insertions(+)
>  create mode 100644 sysdeps/aarch64/fast-jitter.h
>  create mode 100644 sysdeps/alpha/fast-jitter.h
>  create mode 100644 sysdeps/generic/fast-jitter.h
>  create mode 100644 sysdeps/s390/fast-jitter.h
>  create mode 100644 sysdeps/sparc/fast-jitter.h
>  create mode 100644 sysdeps/x86_64/fast-jitter.h
> 
> diff --git a/sysdeps/aarch64/fast-jitter.h b/sysdeps/aarch64/fast-jitter.h
> new file mode 100644
> index 0000000000..fb09d2632c
> --- /dev/null
> +++ b/sysdeps/aarch64/fast-jitter.h
> @@ -0,0 +1,33 @@
> +/* Fast jitter on arm with HP_TIMING_NOW
> +   Copyright (C) 2022-2022 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <https://www.gnu.org/licenses/>.  */
> +
> +#ifndef _FAST_JITTER_H
> +# define _FAST_JITTER_H
> +
> +#include <stdint.h>
> +#include <hp-timing.h>
> +
> +static inline uint32_t
> +get_fast_jitter (void)
> +{
> +  hp_timing_t jitter;
> +  HP_TIMING_NOW (jitter);
> +  return (uint32_t) jitter;
> +}
> +
> +#endif
> diff --git a/sysdeps/alpha/fast-jitter.h b/sysdeps/alpha/fast-jitter.h
> new file mode 100644
> index 0000000000..0a24290eaa
> --- /dev/null
> +++ b/sysdeps/alpha/fast-jitter.h
> @@ -0,0 +1,34 @@
> +/* Fast jitter on alpha with rpcc
> +   Copyright (C) 2022-2022 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <https://www.gnu.org/licenses/>.  */
> +
> +#ifndef _FAST_JITTER_H
> +# define _FAST_JITTER_H
> +
> +#include <stdint.h>
> +
> +static inline uint32_t
> +get_fast_jitter (void)
> +{
> +  unsigned long int x_;
> +  asm volatile ("rpcc %0" : "=r"(x_));
> +  /* Don't both with process offset.  We only need jitter not
> +     monotonic cycle count.  */
> +  return (uint32_t) x;
> +}
> +
> +#endif
> diff --git a/sysdeps/generic/fast-jitter.h b/sysdeps/generic/fast-jitter.h
> new file mode 100644
> index 0000000000..63bcf3ccd7
> --- /dev/null
> +++ b/sysdeps/generic/fast-jitter.h
> @@ -0,0 +1,35 @@
> +/* Fallback for fast jitter just return 0.
> +   Copyright (C) 2019-2022 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <https://www.gnu.org/licenses/>.  */
> +
> +#ifndef _FAST_JITTER_H
> +# define _FAST_JITTER_H
> +
> +#include <stdint.h>
> +
> +/* Baseline just return 0.  We could create jitter using a clock or
> +   'random_bits' but that may imply a syscall and the goal of
> +   'get_fast_jitter' is minimal overhead "randomness" when such
> +   randomness helps performance.  Adding high overhead the function
> +   defeats the purpose.  */
> +static inline uint32_t
> +get_fast_jitter (void)
> +{
> +  return 0;
> +}
> +
> +#endif
> diff --git a/sysdeps/s390/fast-jitter.h b/sysdeps/s390/fast-jitter.h
> new file mode 100644
> index 0000000000..eb905b1413
> --- /dev/null
> +++ b/sysdeps/s390/fast-jitter.h
> @@ -0,0 +1,33 @@
> +/* Fast jitter on s390 with HP_TIMING_NOW
> +   Copyright (C) 2022-2022 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <https://www.gnu.org/licenses/>.  */
> +
> +#ifndef _FAST_JITTER_H
> +# define _FAST_JITTER_H
> +
> +#include <stdint.h>
> +#include <hp-timing.h>
> +
> +static inline uint32_t
> +get_fast_jitter (void)
> +{
> +  hp_timing_t jitter;
> +  HP_TIMING_NOW (jitter);
> +  return (uint32_t) jitter;
> +}
> +
> +#endif
> diff --git a/sysdeps/sparc/fast-jitter.h b/sysdeps/sparc/fast-jitter.h
> new file mode 100644
> index 0000000000..f4413754c5
> --- /dev/null
> +++ b/sysdeps/sparc/fast-jitter.h
> @@ -0,0 +1,33 @@
> +/* Fast jitter on sparc with HP_TIMING_NOW
> +   Copyright (C) 2022-2022 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <https://www.gnu.org/licenses/>.  */
> +
> +#ifndef _FAST_JITTER_H
> +# define _FAST_JITTER_H
> +
> +#include <stdint.h>
> +#include <hp-timing.h>
> +
> +static inline uint32_t
> +get_fast_jitter (void)
> +{
> +  hp_timing_t jitter;
> +  HP_TIMING_NOW (jitter);
> +  return (uint32_t) jitter;
> +}
> +
> +#endif
> diff --git a/sysdeps/x86_64/fast-jitter.h b/sysdeps/x86_64/fast-jitter.h
> new file mode 100644
> index 0000000000..1140f1c295
> --- /dev/null
> +++ b/sysdeps/x86_64/fast-jitter.h
> @@ -0,0 +1,30 @@
> +/* X86 use rdtsc to quickly generate pseudo-random for jitter
> +   Copyright (C) 2022-2022 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <https://www.gnu.org/licenses/>.  */
> +
> +#ifndef _FAST_JITTER_H
> +# define _FAST_JITTER_H
> +
> +#include <stdint.h>
> +
> +static inline uint32_t
> +get_fast_jitter (void)
> +{
> +  return __builtin_ia32_rdtsc ();

Why can we use HP_TIMING_NOW for x86 as well?  So you then you can use
only a generic implementation like:

static inline uint32_t
get_fast_jitter (void)
{
#if HP_TIMING_INLINE
  hp_timing_t jitter;
  HP_TIMING_NOW (jitter);
  return (uint32_t) jitter;
#else
  return 0;
#endif
}
  

On Wed, Apr 27, 2022 at 10:48 AM Adhemerval Zanella via Libc-alpha
<libc-alpha@sourceware.org> wrote:
>
>
>
> On 04/04/2022 18:39, Noah Goldstein via Libc-alpha wrote:
> > 'get_fast_jitter' is meant to be used purely for performance
> > purposes. In all cases it's used it should be acceptable to get no
> > randomness (see default case). An example use case is in setting
> > jitter for retries between threads at a lock. There is a
> > performance benefit to having jitter, but only if the jitter can
> > be generated very quickly and ultimately there is no serious issue
> > if no jitter is generated.
> >
> > The implementation generally uses 'HP_TIMING_NOW' or another cycle
> > counter when the architecture supports it. The default case just
> > returns zero.
>
> I think it should ok, although I think it would be better to be sent
> along with a actual usage (as the pthread mutex optimization).
>
> > ---
> >  sysdeps/aarch64/fast-jitter.h | 33 +++++++++++++++++++++++++++++++++
> >  sysdeps/alpha/fast-jitter.h   | 34 ++++++++++++++++++++++++++++++++++
> >  sysdeps/generic/fast-jitter.h | 35 +++++++++++++++++++++++++++++++++++
> >  sysdeps/s390/fast-jitter.h    | 33 +++++++++++++++++++++++++++++++++
> >  sysdeps/sparc/fast-jitter.h   | 33 +++++++++++++++++++++++++++++++++
> >  sysdeps/x86_64/fast-jitter.h  | 30 ++++++++++++++++++++++++++++++
> >  6 files changed, 198 insertions(+)
> >  create mode 100644 sysdeps/aarch64/fast-jitter.h
> >  create mode 100644 sysdeps/alpha/fast-jitter.h
> >  create mode 100644 sysdeps/generic/fast-jitter.h
> >  create mode 100644 sysdeps/s390/fast-jitter.h
> >  create mode 100644 sysdeps/sparc/fast-jitter.h
> >  create mode 100644 sysdeps/x86_64/fast-jitter.h
> >
> > diff --git a/sysdeps/aarch64/fast-jitter.h b/sysdeps/aarch64/fast-jitter.h
> > new file mode 100644
> > index 0000000000..fb09d2632c
> > --- /dev/null
> > +++ b/sysdeps/aarch64/fast-jitter.h
> > @@ -0,0 +1,33 @@
> > +/* Fast jitter on arm with HP_TIMING_NOW
> > +   Copyright (C) 2022-2022 Free Software Foundation, Inc.
> > +   This file is part of the GNU C Library.
> > +
> > +   The GNU C Library is free software; you can redistribute it and/or
> > +   modify it under the terms of the GNU Lesser General Public
> > +   License as published by the Free Software Foundation; either
> > +   version 2.1 of the License, or (at your option) any later version.
> > +
> > +   The GNU C Library is distributed in the hope that it will be useful,
> > +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> > +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> > +   Lesser General Public License for more details.
> > +
> > +   You should have received a copy of the GNU Lesser General Public
> > +   License along with the GNU C Library; if not, see
> > +   <https://www.gnu.org/licenses/>.  */
> > +
> > +#ifndef _FAST_JITTER_H
> > +# define _FAST_JITTER_H
> > +
> > +#include <stdint.h>
> > +#include <hp-timing.h>
> > +
> > +static inline uint32_t
> > +get_fast_jitter (void)
> > +{
> > +  hp_timing_t jitter;
> > +  HP_TIMING_NOW (jitter);
> > +  return (uint32_t) jitter;
> > +}
> > +
> > +#endif
> > diff --git a/sysdeps/alpha/fast-jitter.h b/sysdeps/alpha/fast-jitter.h
> > new file mode 100644
> > index 0000000000..0a24290eaa
> > --- /dev/null
> > +++ b/sysdeps/alpha/fast-jitter.h
> > @@ -0,0 +1,34 @@
> > +/* Fast jitter on alpha with rpcc
> > +   Copyright (C) 2022-2022 Free Software Foundation, Inc.
> > +   This file is part of the GNU C Library.
> > +
> > +   The GNU C Library is free software; you can redistribute it and/or
> > +   modify it under the terms of the GNU Lesser General Public
> > +   License as published by the Free Software Foundation; either
> > +   version 2.1 of the License, or (at your option) any later version.
> > +
> > +   The GNU C Library is distributed in the hope that it will be useful,
> > +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> > +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> > +   Lesser General Public License for more details.
> > +
> > +   You should have received a copy of the GNU Lesser General Public
> > +   License along with the GNU C Library; if not, see
> > +   <https://www.gnu.org/licenses/>.  */
> > +
> > +#ifndef _FAST_JITTER_H
> > +# define _FAST_JITTER_H
> > +
> > +#include <stdint.h>
> > +
> > +static inline uint32_t
> > +get_fast_jitter (void)
> > +{
> > +  unsigned long int x_;
> > +  asm volatile ("rpcc %0" : "=r"(x_));
> > +  /* Don't both with process offset.  We only need jitter not
> > +     monotonic cycle count.  */
> > +  return (uint32_t) x;
> > +}
> > +
> > +#endif
> > diff --git a/sysdeps/generic/fast-jitter.h b/sysdeps/generic/fast-jitter.h
> > new file mode 100644
> > index 0000000000..63bcf3ccd7
> > --- /dev/null
> > +++ b/sysdeps/generic/fast-jitter.h
> > @@ -0,0 +1,35 @@
> > +/* Fallback for fast jitter just return 0.
> > +   Copyright (C) 2019-2022 Free Software Foundation, Inc.
> > +   This file is part of the GNU C Library.
> > +
> > +   The GNU C Library is free software; you can redistribute it and/or
> > +   modify it under the terms of the GNU Lesser General Public
> > +   License as published by the Free Software Foundation; either
> > +   version 2.1 of the License, or (at your option) any later version.
> > +
> > +   The GNU C Library is distributed in the hope that it will be useful,
> > +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> > +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> > +   Lesser General Public License for more details.
> > +
> > +   You should have received a copy of the GNU Lesser General Public
> > +   License along with the GNU C Library; if not, see
> > +   <https://www.gnu.org/licenses/>.  */
> > +
> > +#ifndef _FAST_JITTER_H
> > +# define _FAST_JITTER_H
> > +
> > +#include <stdint.h>
> > +
> > +/* Baseline just return 0.  We could create jitter using a clock or
> > +   'random_bits' but that may imply a syscall and the goal of
> > +   'get_fast_jitter' is minimal overhead "randomness" when such
> > +   randomness helps performance.  Adding high overhead the function
> > +   defeats the purpose.  */
> > +static inline uint32_t
> > +get_fast_jitter (void)
> > +{
> > +  return 0;
> > +}
> > +
> > +#endif
> > diff --git a/sysdeps/s390/fast-jitter.h b/sysdeps/s390/fast-jitter.h
> > new file mode 100644
> > index 0000000000..eb905b1413
> > --- /dev/null
> > +++ b/sysdeps/s390/fast-jitter.h
> > @@ -0,0 +1,33 @@
> > +/* Fast jitter on s390 with HP_TIMING_NOW
> > +   Copyright (C) 2022-2022 Free Software Foundation, Inc.
> > +   This file is part of the GNU C Library.
> > +
> > +   The GNU C Library is free software; you can redistribute it and/or
> > +   modify it under the terms of the GNU Lesser General Public
> > +   License as published by the Free Software Foundation; either
> > +   version 2.1 of the License, or (at your option) any later version.
> > +
> > +   The GNU C Library is distributed in the hope that it will be useful,
> > +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> > +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> > +   Lesser General Public License for more details.
> > +
> > +   You should have received a copy of the GNU Lesser General Public
> > +   License along with the GNU C Library; if not, see
> > +   <https://www.gnu.org/licenses/>.  */
> > +
> > +#ifndef _FAST_JITTER_H
> > +# define _FAST_JITTER_H
> > +
> > +#include <stdint.h>
> > +#include <hp-timing.h>
> > +
> > +static inline uint32_t
> > +get_fast_jitter (void)
> > +{
> > +  hp_timing_t jitter;
> > +  HP_TIMING_NOW (jitter);
> > +  return (uint32_t) jitter;
> > +}
> > +
> > +#endif
> > diff --git a/sysdeps/sparc/fast-jitter.h b/sysdeps/sparc/fast-jitter.h
> > new file mode 100644
> > index 0000000000..f4413754c5
> > --- /dev/null
> > +++ b/sysdeps/sparc/fast-jitter.h
> > @@ -0,0 +1,33 @@
> > +/* Fast jitter on sparc with HP_TIMING_NOW
> > +   Copyright (C) 2022-2022 Free Software Foundation, Inc.
> > +   This file is part of the GNU C Library.
> > +
> > +   The GNU C Library is free software; you can redistribute it and/or
> > +   modify it under the terms of the GNU Lesser General Public
> > +   License as published by the Free Software Foundation; either
> > +   version 2.1 of the License, or (at your option) any later version.
> > +
> > +   The GNU C Library is distributed in the hope that it will be useful,
> > +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> > +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> > +   Lesser General Public License for more details.
> > +
> > +   You should have received a copy of the GNU Lesser General Public
> > +   License along with the GNU C Library; if not, see
> > +   <https://www.gnu.org/licenses/>.  */
> > +
> > +#ifndef _FAST_JITTER_H
> > +# define _FAST_JITTER_H
> > +
> > +#include <stdint.h>
> > +#include <hp-timing.h>
> > +
> > +static inline uint32_t
> > +get_fast_jitter (void)
> > +{
> > +  hp_timing_t jitter;
> > +  HP_TIMING_NOW (jitter);
> > +  return (uint32_t) jitter;
> > +}
> > +
> > +#endif
> > diff --git a/sysdeps/x86_64/fast-jitter.h b/sysdeps/x86_64/fast-jitter.h
> > new file mode 100644
> > index 0000000000..1140f1c295
> > --- /dev/null
> > +++ b/sysdeps/x86_64/fast-jitter.h
> > @@ -0,0 +1,30 @@
> > +/* X86 use rdtsc to quickly generate pseudo-random for jitter
> > +   Copyright (C) 2022-2022 Free Software Foundation, Inc.
> > +   This file is part of the GNU C Library.
> > +
> > +   The GNU C Library is free software; you can redistribute it and/or
> > +   modify it under the terms of the GNU Lesser General Public
> > +   License as published by the Free Software Foundation; either
> > +   version 2.1 of the License, or (at your option) any later version.
> > +
> > +   The GNU C Library is distributed in the hope that it will be useful,
> > +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> > +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> > +   Lesser General Public License for more details.
> > +
> > +   You should have received a copy of the GNU Lesser General Public
> > +   License along with the GNU C Library; if not, see
> > +   <https://www.gnu.org/licenses/>.  */
> > +
> > +#ifndef _FAST_JITTER_H
> > +# define _FAST_JITTER_H
> > +
> > +#include <stdint.h>
> > +
> > +static inline uint32_t
> > +get_fast_jitter (void)
> > +{
> > +  return __builtin_ia32_rdtsc ();
>
> Why can we use HP_TIMING_NOW for x86 as well?  So you then you can use
> only a generic implementation like:
>
> static inline uint32_t
> get_fast_jitter (void)
> {
> #if HP_TIMING_INLINE
>   hp_timing_t jitter;
>   HP_TIMING_NOW (jitter);
>   return (uint32_t) jitter;
> #else
>   return 0;
> #endif
> }

I'd like this version.  Noah, can you send v2?

Thanks,
  

On Wed, Apr 27, 2022 at 1:05 PM H.J. Lu <hjl.tools@gmail.com> wrote:
>
> On Wed, Apr 27, 2022 at 10:48 AM Adhemerval Zanella via Libc-alpha
> <libc-alpha@sourceware.org> wrote:
> >
> >
> >
> > On 04/04/2022 18:39, Noah Goldstein via Libc-alpha wrote:
> > > 'get_fast_jitter' is meant to be used purely for performance
> > > purposes. In all cases it's used it should be acceptable to get no
> > > randomness (see default case). An example use case is in setting
> > > jitter for retries between threads at a lock. There is a
> > > performance benefit to having jitter, but only if the jitter can
> > > be generated very quickly and ultimately there is no serious issue
> > > if no jitter is generated.
> > >
> > > The implementation generally uses 'HP_TIMING_NOW' or another cycle
> > > counter when the architecture supports it. The default case just
> > > returns zero.
> >
> > I think it should ok, although I think it would be better to be sent
> > along with a actual usage (as the pthread mutex optimization).


> >
> > > ---
> > >  sysdeps/aarch64/fast-jitter.h | 33 +++++++++++++++++++++++++++++++++
> > >  sysdeps/alpha/fast-jitter.h   | 34 ++++++++++++++++++++++++++++++++++
> > >  sysdeps/generic/fast-jitter.h | 35 +++++++++++++++++++++++++++++++++++
> > >  sysdeps/s390/fast-jitter.h    | 33 +++++++++++++++++++++++++++++++++
> > >  sysdeps/sparc/fast-jitter.h   | 33 +++++++++++++++++++++++++++++++++
> > >  sysdeps/x86_64/fast-jitter.h  | 30 ++++++++++++++++++++++++++++++
> > >  6 files changed, 198 insertions(+)
> > >  create mode 100644 sysdeps/aarch64/fast-jitter.h
> > >  create mode 100644 sysdeps/alpha/fast-jitter.h
> > >  create mode 100644 sysdeps/generic/fast-jitter.h
> > >  create mode 100644 sysdeps/s390/fast-jitter.h
> > >  create mode 100644 sysdeps/sparc/fast-jitter.h
> > >  create mode 100644 sysdeps/x86_64/fast-jitter.h
> > >
> > > diff --git a/sysdeps/aarch64/fast-jitter.h b/sysdeps/aarch64/fast-jitter.h
> > > new file mode 100644
> > > index 0000000000..fb09d2632c
> > > --- /dev/null
> > > +++ b/sysdeps/aarch64/fast-jitter.h
> > > @@ -0,0 +1,33 @@
> > > +/* Fast jitter on arm with HP_TIMING_NOW
> > > +   Copyright (C) 2022-2022 Free Software Foundation, Inc.
> > > +   This file is part of the GNU C Library.
> > > +
> > > +   The GNU C Library is free software; you can redistribute it and/or
> > > +   modify it under the terms of the GNU Lesser General Public
> > > +   License as published by the Free Software Foundation; either
> > > +   version 2.1 of the License, or (at your option) any later version.
> > > +
> > > +   The GNU C Library is distributed in the hope that it will be useful,
> > > +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> > > +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> > > +   Lesser General Public License for more details.
> > > +
> > > +   You should have received a copy of the GNU Lesser General Public
> > > +   License along with the GNU C Library; if not, see
> > > +   <https://www.gnu.org/licenses/>.  */
> > > +
> > > +#ifndef _FAST_JITTER_H
> > > +# define _FAST_JITTER_H
> > > +
> > > +#include <stdint.h>
> > > +#include <hp-timing.h>
> > > +
> > > +static inline uint32_t
> > > +get_fast_jitter (void)
> > > +{
> > > +  hp_timing_t jitter;
> > > +  HP_TIMING_NOW (jitter);
> > > +  return (uint32_t) jitter;
> > > +}
> > > +
> > > +#endif
> > > diff --git a/sysdeps/alpha/fast-jitter.h b/sysdeps/alpha/fast-jitter.h
> > > new file mode 100644
> > > index 0000000000..0a24290eaa
> > > --- /dev/null
> > > +++ b/sysdeps/alpha/fast-jitter.h
> > > @@ -0,0 +1,34 @@
> > > +/* Fast jitter on alpha with rpcc
> > > +   Copyright (C) 2022-2022 Free Software Foundation, Inc.
> > > +   This file is part of the GNU C Library.
> > > +
> > > +   The GNU C Library is free software; you can redistribute it and/or
> > > +   modify it under the terms of the GNU Lesser General Public
> > > +   License as published by the Free Software Foundation; either
> > > +   version 2.1 of the License, or (at your option) any later version.
> > > +
> > > +   The GNU C Library is distributed in the hope that it will be useful,
> > > +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> > > +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> > > +   Lesser General Public License for more details.
> > > +
> > > +   You should have received a copy of the GNU Lesser General Public
> > > +   License along with the GNU C Library; if not, see
> > > +   <https://www.gnu.org/licenses/>.  */
> > > +
> > > +#ifndef _FAST_JITTER_H
> > > +# define _FAST_JITTER_H
> > > +
> > > +#include <stdint.h>
> > > +
> > > +static inline uint32_t
> > > +get_fast_jitter (void)
> > > +{
> > > +  unsigned long int x_;
> > > +  asm volatile ("rpcc %0" : "=r"(x_));
> > > +  /* Don't both with process offset.  We only need jitter not
> > > +     monotonic cycle count.  */
> > > +  return (uint32_t) x;
> > > +}
> > > +
> > > +#endif
> > > diff --git a/sysdeps/generic/fast-jitter.h b/sysdeps/generic/fast-jitter.h
> > > new file mode 100644
> > > index 0000000000..63bcf3ccd7
> > > --- /dev/null
> > > +++ b/sysdeps/generic/fast-jitter.h
> > > @@ -0,0 +1,35 @@
> > > +/* Fallback for fast jitter just return 0.
> > > +   Copyright (C) 2019-2022 Free Software Foundation, Inc.
> > > +   This file is part of the GNU C Library.
> > > +
> > > +   The GNU C Library is free software; you can redistribute it and/or
> > > +   modify it under the terms of the GNU Lesser General Public
> > > +   License as published by the Free Software Foundation; either
> > > +   version 2.1 of the License, or (at your option) any later version.
> > > +
> > > +   The GNU C Library is distributed in the hope that it will be useful,
> > > +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> > > +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> > > +   Lesser General Public License for more details.
> > > +
> > > +   You should have received a copy of the GNU Lesser General Public
> > > +   License along with the GNU C Library; if not, see
> > > +   <https://www.gnu.org/licenses/>.  */
> > > +
> > > +#ifndef _FAST_JITTER_H
> > > +# define _FAST_JITTER_H
> > > +
> > > +#include <stdint.h>
> > > +
> > > +/* Baseline just return 0.  We could create jitter using a clock or
> > > +   'random_bits' but that may imply a syscall and the goal of
> > > +   'get_fast_jitter' is minimal overhead "randomness" when such
> > > +   randomness helps performance.  Adding high overhead the function
> > > +   defeats the purpose.  */
> > > +static inline uint32_t
> > > +get_fast_jitter (void)
> > > +{
> > > +  return 0;
> > > +}
> > > +
> > > +#endif
> > > diff --git a/sysdeps/s390/fast-jitter.h b/sysdeps/s390/fast-jitter.h
> > > new file mode 100644
> > > index 0000000000..eb905b1413
> > > --- /dev/null
> > > +++ b/sysdeps/s390/fast-jitter.h
> > > @@ -0,0 +1,33 @@
> > > +/* Fast jitter on s390 with HP_TIMING_NOW
> > > +   Copyright (C) 2022-2022 Free Software Foundation, Inc.
> > > +   This file is part of the GNU C Library.
> > > +
> > > +   The GNU C Library is free software; you can redistribute it and/or
> > > +   modify it under the terms of the GNU Lesser General Public
> > > +   License as published by the Free Software Foundation; either
> > > +   version 2.1 of the License, or (at your option) any later version.
> > > +
> > > +   The GNU C Library is distributed in the hope that it will be useful,
> > > +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> > > +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> > > +   Lesser General Public License for more details.
> > > +
> > > +   You should have received a copy of the GNU Lesser General Public
> > > +   License along with the GNU C Library; if not, see
> > > +   <https://www.gnu.org/licenses/>.  */
> > > +
> > > +#ifndef _FAST_JITTER_H
> > > +# define _FAST_JITTER_H
> > > +
> > > +#include <stdint.h>
> > > +#include <hp-timing.h>
> > > +
> > > +static inline uint32_t
> > > +get_fast_jitter (void)
> > > +{
> > > +  hp_timing_t jitter;
> > > +  HP_TIMING_NOW (jitter);
> > > +  return (uint32_t) jitter;
> > > +}
> > > +
> > > +#endif
> > > diff --git a/sysdeps/sparc/fast-jitter.h b/sysdeps/sparc/fast-jitter.h
> > > new file mode 100644
> > > index 0000000000..f4413754c5
> > > --- /dev/null
> > > +++ b/sysdeps/sparc/fast-jitter.h
> > > @@ -0,0 +1,33 @@
> > > +/* Fast jitter on sparc with HP_TIMING_NOW
> > > +   Copyright (C) 2022-2022 Free Software Foundation, Inc.
> > > +   This file is part of the GNU C Library.
> > > +
> > > +   The GNU C Library is free software; you can redistribute it and/or
> > > +   modify it under the terms of the GNU Lesser General Public
> > > +   License as published by the Free Software Foundation; either
> > > +   version 2.1 of the License, or (at your option) any later version.
> > > +
> > > +   The GNU C Library is distributed in the hope that it will be useful,
> > > +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> > > +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> > > +   Lesser General Public License for more details.
> > > +
> > > +   You should have received a copy of the GNU Lesser General Public
> > > +   License along with the GNU C Library; if not, see
> > > +   <https://www.gnu.org/licenses/>.  */
> > > +
> > > +#ifndef _FAST_JITTER_H
> > > +# define _FAST_JITTER_H
> > > +
> > > +#include <stdint.h>
> > > +#include <hp-timing.h>
> > > +
> > > +static inline uint32_t
> > > +get_fast_jitter (void)
> > > +{
> > > +  hp_timing_t jitter;
> > > +  HP_TIMING_NOW (jitter);
> > > +  return (uint32_t) jitter;
> > > +}
> > > +
> > > +#endif
> > > diff --git a/sysdeps/x86_64/fast-jitter.h b/sysdeps/x86_64/fast-jitter.h
> > > new file mode 100644
> > > index 0000000000..1140f1c295
> > > --- /dev/null
> > > +++ b/sysdeps/x86_64/fast-jitter.h
> > > @@ -0,0 +1,30 @@
> > > +/* X86 use rdtsc to quickly generate pseudo-random for jitter
> > > +   Copyright (C) 2022-2022 Free Software Foundation, Inc.
> > > +   This file is part of the GNU C Library.
> > > +
> > > +   The GNU C Library is free software; you can redistribute it and/or
> > > +   modify it under the terms of the GNU Lesser General Public
> > > +   License as published by the Free Software Foundation; either
> > > +   version 2.1 of the License, or (at your option) any later version.
> > > +
> > > +   The GNU C Library is distributed in the hope that it will be useful,
> > > +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> > > +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> > > +   Lesser General Public License for more details.
> > > +
> > > +   You should have received a copy of the GNU Lesser General Public
> > > +   License along with the GNU C Library; if not, see
> > > +   <https://www.gnu.org/licenses/>.  */
> > > +
> > > +#ifndef _FAST_JITTER_H
> > > +# define _FAST_JITTER_H
> > > +
> > > +#include <stdint.h>
> > > +
> > > +static inline uint32_t
> > > +get_fast_jitter (void)
> > > +{
> > > +  return __builtin_ia32_rdtsc ();
> >
> > Why can we use HP_TIMING_NOW for x86 as well?  So you then you can use
> > only a generic implementation like:
> >
> > static inline uint32_t
> > get_fast_jitter (void)
> > {
> > #if HP_TIMING_INLINE
> >   hp_timing_t jitter;
> >   HP_TIMING_NOW (jitter);
> >   return (uint32_t) jitter;
> > #else
> >   return 0;
> > #endif
> > }
>
> I'd like this version.  Noah, can you send v2?
>

Fixed in V2, alpha arch will be slower but otherwise should be the same.

> Thanks,

>
> --
> H.J.