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Re: [PATCH v6 1/3] Tunables: Add tunables of spin count for pthread adaptive spin mutex


On Mon, Jul 2, 2018 at 1:27 AM, Kemi Wang <kemi.wang@intel.com> wrote:
> This patch does not have any functionality change, we only provide a spin
> count tunes for pthread adaptive spin mutex. The tunable
> glibc.mutex.spin_count tunes can be used by system administrator to squeeze
> system performance according to different hardware capabilities and
> workload characteristics.
>
> The maximum value of spin count is limited to 30000 to avoid the overflow
> of mutex->__data.__spins variable with the possible type of short in
> pthread_mutex_lock ().
>
> The default value of spin count is set to 100 with the reference to the
> previous number of times of spinning via trylock. This value would be
> architecture-specific and can be tuned with kinds of benchmarks to fit most
> cases in future.
>
> This is the preparation work for the next patch, in which the way of
> adaptive spin would be changed from an expensive cmpxchg to read while
> spinning.
>
>    * elf/dl-tunables.list: Add glibc.mutex.spin_count entry.
>    * manual/tunables.texi: Add glibc.mutex.spin_count description.
>    * nptl/Makefile: Add pthread_mutex_conf.c for compilation.
>    * nptl/pthread_mutex_conf.h: New file.
>    * nptl/pthread_mutex_conf.c: New file.
>    * nptl/nptl-init.c: Put mutex tunable initialization in pthread
>      initialization.
>
> ChangeLog:
>     V5->V6:
>     a) Missing "pthread mutex tunables" entry in the menu of tunables.texi,
>     add it.
>
>     V4->V5
>     a) Put mutex tunable (glibc.mutex.spin_count) initialization as part of
>     overall pthread initialization, that would avoid the extra relocation,
>     as suggested by Florian Weimer. Thanks for pointing it out!
>     b) Move the READ_ONLY_SPIN macro definition from the third patch to
>     this patch
>
>     V3->V4
>     a) Add comments in elf/dl-tunables.list
>
>     V2->V3
>     a) Polish the description of glibc.mutex.spin_count tunable with the
>     help from Rical Jasan.
>     b) Get rid of the TUNABLE_CALLBACK_FNDECL macros in
>     pthread_mutex_conf.c, as suggested by Florian Weimer.
>     c) Adjust the default value of spin count to 100 with the reference of
>     the previous spinning way via trylock.
>
>     V1->V2
>     a) Renamed nptl/mutex-conf.h -> nptl/pthread_mutex_conf.h
>     b) Renamed nptl/mutex-conf.c -> nptl/pthread_mutex_conf.c
>     c) Change the Makefile to compile pthread_mutex_conf.c
>     d) Modify the copyright "2013-2018" -> "2018" for new added files
>     e) Fix the indentation issue (tab -> double space) in
>     elf/dl-tunables.list
>     f) Remove the env alias LD_SPIN_COUNT in elf/dl-tunables.list
>     g) Fix the typo errors and refresh glibc.mutex.spin_count tunable
>     description in manual/tunables.texi.
>     h) Fix the indentation issue in nptl/pthread_mutex_conf.c
>     i) Fix the indentation issue for nested preprocessor (add one space for
>     each level)
>
> Suggested-by: Andi Kleen <andi.kleen@intel.com>
> Signed-off-by: Kemi Wang <kemi.wang@intel.com>
> ---
>  elf/dl-tunables.list      | 17 ++++++++++++++
>  manual/tunables.texi      | 23 +++++++++++++++++++
>  nptl/Makefile             |  3 ++-
>  nptl/nptl-init.c          |  5 +++++
>  nptl/pthread_mutex_conf.c | 57 +++++++++++++++++++++++++++++++++++++++++++++++
>  nptl/pthread_mutex_conf.h | 35 +++++++++++++++++++++++++++++
>  6 files changed, 139 insertions(+), 1 deletion(-)
>  create mode 100644 nptl/pthread_mutex_conf.c
>  create mode 100644 nptl/pthread_mutex_conf.h
>
> diff --git a/elf/dl-tunables.list b/elf/dl-tunables.list
> index 1f8ecb8..2c5a13f 100644
> --- a/elf/dl-tunables.list
> +++ b/elf/dl-tunables.list
> @@ -121,4 +121,21 @@ glibc {
>        default: 3
>      }
>    }
> +
> +# The maximum value of spin count is limited to 30000 to avoid the overflow
> +# of mutex->__data.__spins variable with the possible type of short in
> +# pthread_mutex_lock ().
> +#
> +# The default value of spin count is set to 100 with the reference to the
> +# previous number of times of spinning via trylock. This value would be
> +# architecture-specific and can be tuned with kinds of benchmarks to fit
> +# most cases in future.
> +  mutex {
> +    spin_count {
> +      type: INT_32
> +      minval: 0
> +      maxval: 30000
> +      default: 100
> +    }
> +  }
>  }
> diff --git a/manual/tunables.texi b/manual/tunables.texi
> index be33c9f..f660604 100644
> --- a/manual/tunables.texi
> +++ b/manual/tunables.texi
> @@ -32,6 +32,7 @@ their own namespace.
>  * Tunable names::  The structure of a tunable name
>  * Memory Allocation Tunables::  Tunables in the memory allocation subsystem
>  * Elision Tunables::  Tunables in elision subsystem
> +* Pthread Mutex Tunables:: Tunables in mutex
>  * Hardware Capability Tunables::  Tunables that modify the hardware
>                                   capabilities seen by @theglibc{}
>  @end menu
> @@ -281,6 +282,28 @@ of try lock attempts.
>  The default value of this tunable is @samp{3}.
>  @end deftp
>
> +@node Pthread Mutex Tunables
> +@section Pthread Mutex Tunables
> +@cindex pthread mutex tunables
> +
> +@deftp {Tunable namespace} glibc.mutex
> +The behavior of pthread mutexes can be tuned to gain performance improvements
> +according to specific hardware capabilities and workload characteristics by
> +setting the following tunables in the @code{mutex} namespace:
> +@end deftp
> +
> +@deftp Tunable glibc.mutex.spin_count
> +The @code{glibc.mutex.spin_count} tunable sets the maximum number of times
> +a thread should spin on the lock before calling into the kernel to block.
> +Adaptive spin is used for mutexes initialized with the PTHREAD_MUTEX_ADAPTIVE_NP
> +GNU extension.  It affects both pthread_mutex_lock and pthread_mutex_timedlock.
> +
> +The spinning is done until either the maximum spin times is reached or
> +the lock is acquired.
> +
> +The default value of this tunable is @samp{100}.
> +@end deftp
> +
>  @node Hardware Capability Tunables
>  @section Hardware Capability Tunables
>  @cindex hardware capability tunables
> diff --git a/nptl/Makefile b/nptl/Makefile
> index 94be92c..bd1096f 100644
> --- a/nptl/Makefile
> +++ b/nptl/Makefile
> @@ -139,7 +139,8 @@ libpthread-routines = nptl-init vars events version pt-interp \
>                       pthread_mutex_getprioceiling \
>                       pthread_mutex_setprioceiling \
>                       pthread_setname pthread_getname \
> -                     pthread_setattr_default_np pthread_getattr_default_np
> +                     pthread_setattr_default_np pthread_getattr_default_np \
> +                     pthread_mutex_conf
>  #                    pthread_setuid pthread_seteuid pthread_setreuid \
>  #                    pthread_setresuid \
>  #                    pthread_setgid pthread_setegid pthread_setregid \
> diff --git a/nptl/nptl-init.c b/nptl/nptl-init.c
> index 1d3790f..3e6e2e1 100644
> --- a/nptl/nptl-init.c
> +++ b/nptl/nptl-init.c
> @@ -38,6 +38,7 @@
>  #include <kernel-features.h>
>  #include <libc-pointer-arith.h>
>  #include <pthread-pids.h>
> +#include <pthread_mutex_conf.h>
>
>  #ifndef TLS_MULTIPLE_THREADS_IN_TCB
>  /* Pointer to the corresponding variable in libc.  */
> @@ -446,6 +447,10 @@ __pthread_initialize_minimal_internal (void)
>
>    /* Determine whether the machine is SMP or not.  */
>    __is_smp = is_smp_system ();
> +
> +#if HAVE_TUNABLES
> +  mutex_tunables_init ();
> +#endif
>  }
>  strong_alias (__pthread_initialize_minimal_internal,
>               __pthread_initialize_minimal)
> diff --git a/nptl/pthread_mutex_conf.c b/nptl/pthread_mutex_conf.c
> new file mode 100644
> index 0000000..9b2c5d1
> --- /dev/null
> +++ b/nptl/pthread_mutex_conf.c
> @@ -0,0 +1,57 @@
> +/* pthread_mutex_conf.c: Pthread mutex tunable parameters.
> +   Copyright (C) 2018 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
> +   <http://www.gnu.org/licenses/>.  */
> +
> +#include "config.h"
> +#include <pthreadP.h>
> +#include <init-arch.h>
> +#include <pthread_mutex_conf.h>
> +#include <unistd.h>
> +
> +#if HAVE_TUNABLES
> +# define TUNABLE_NAMESPACE mutex
> +#endif
> +#include <elf/dl-tunables.h>
> +
> +
> +struct mutex_config __mutex_aconf =
> +{
> +  /* The maximum number of times a thread should spin on the lock before
> +  calling into kernel to block.  */
> +  .spin_count = 100,

Replace 100 with MAX_ADAPTIVE_COUNT.

> +};
> +

Move it before #if HAVE_TUNABLES.

> +#if HAVE_TUNABLES
> +static inline void __always_inline
> +do_set_mutex_spin_count (int32_t value)
> +{
> +  __mutex_aconf.spin_count = value;
> +}
> +
> +void
> +TUNABLE_CALLBACK (set_mutex_spin_count) (tunable_val_t *valp)
> +{
> +  int32_t value = (int32_t) (valp)->numval;
> +  do_set_mutex_spin_count (value);

Just inline do_set_mutex_spin_count by hand.

> +}
> +
> +void mutex_tunables_init (void)
> +{
> +  TUNABLE_GET (spin_count, int32_t,
> +               TUNABLE_CALLBACK (set_mutex_spin_count));
> +}
> +#endif
> diff --git a/nptl/pthread_mutex_conf.h b/nptl/pthread_mutex_conf.h
> new file mode 100644
> index 0000000..74a0735
> --- /dev/null
> +++ b/nptl/pthread_mutex_conf.h
> @@ -0,0 +1,35 @@
> +/* pthread_mutex_conf.h: Pthread mutex tunable parameters.
> +   Copyright (C) 2018 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
> +   <http://www.gnu.org/licenses/>.  */
> +#ifndef _PTHREAD_MUTEX_CONF_H
> +#define _PTHREAD_MUTEX_CONF_H 1
> +
> +#include <pthread.h>
> +#include <time.h>
> +
> +struct mutex_config
> +{
> +  int spin_count;
> +};
> +
> +extern struct mutex_config __mutex_aconf attribute_hidden;
> +
> +void mutex_tunables_init (void);
> +
> +#define READ_ONLY_SPIN 1

Is READ_ONLY_SPIN always defined to 1?

> +#endif
> --
> 2.7.4
>



-- 
H.J.


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