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Re: [RESEND PATCH v9] Mutex: Add pthread mutex tunables



On 21/11/2018 23:45, Kemi Wang wrote:
> This patch does not have any functionality change, we only provide a spin
> count tunes for pthread adaptive spin mutex. The tunable
> glibc.pthread.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 ().

With current algorithm nptl/pthread_mutex_{timed}lock.c, I think we can use 
the full short range (32767) since assuming maximum spin_nop usage with 'cnt'
being 'max_cnt - 1' (the fast atomic path) it will converge to 32719.

> 
> 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.
> 
>    * sysdeps/nptl/dl-tunables.list: Add glibc.pthread.mutex_spin_count entry.
>    * manual/tunables.texi: Add glibc.pthread.mutex_spin_count description.
>    * nptl/pthread_mutex_conf.h: New file.
>    * nptl/pthread_mutex_conf.c: New file.
>    * nptl/Makefile: Add pthread_mutex_conf.c for compilation.
>    * nptl/nptl-init.c: Put pthread mutex tunable initialization in pthread
>      initialization.
>    * nptl/pthreadP.h: Refine MAX_ADAPTIVE_COUNT macro definition
> 
> I would extend my appreciation sincerely to H.J.Lu for his help to refine
> this patch series.
> 
> ChangeLog:
>     V8->V9:
> 	a) Add the "unistd.h" header file back, or it will cause build
> 	regression on 32 bits system.
> 	b) Rebase on the latest master branch
> 	c) Tested on x86_64 with build-many-glibcs.py
> 
>     V7->V8:
> 	a) Refine the pthread tunables description in manual/tunables.texi
> 	accordingly to Carlos O'Donell and Rical Jason.
> 
>     V6->V7:
>     a) Patch is refined by H.J.Lu
> 
>     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>
> ---
>  manual/tunables.texi          | 27 +++++++++++++++++++++++
>  nptl/Makefile                 |  2 +-
>  nptl/nptl-init.c              |  5 +++++
>  nptl/pthreadP.h               | 24 +++++++++++++++-----
>  nptl/pthread_mutex_conf.c     | 27 +++++++++++++++++++++++
>  nptl/pthread_mutex_conf.h     | 45 ++++++++++++++++++++++++++++++++++++++
>  sysdeps/nptl/dl-tunables.list | 51 +++++++++++++++++++++++++++++++++++++++++++
>  7 files changed, 174 insertions(+), 7 deletions(-)
>  create mode 100644 nptl/pthread_mutex_conf.c
>  create mode 100644 nptl/pthread_mutex_conf.h
>  create mode 100644 sysdeps/nptl/dl-tunables.list
> 
> diff --git a/manual/tunables.texi b/manual/tunables.texi
> index 3345a23..33fbe1e 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
> +* POSIX Thread Tunables:: Tunables in the POSIX thread subsystem
>  * Hardware Capability Tunables::  Tunables that modify the hardware
>  				  capabilities seen by @theglibc{}
>  @end menu
> @@ -281,6 +282,32 @@ of try lock attempts.
>  The default value of this tunable is @samp{3}.
>  @end deftp
>  
> +@node POSIX Thread Tunables
> +@section POSIX Thread Tunables
> +@cindex pthread mutex tunables
> +@cindex thread mutex tunables
> +@cindex mutex tunables
> +@cindex tunables thread mutex
> +
> +@deftp {Tunable namespace} glibc.pthread
> +The behavior of POSIX thread can be tuned to gain performance improvements
> +according to specific hardware capabilities and workload characteristics by
> +setting the following tunables in the @code{pthread} namespace:
> +@end deftp
> +
> +@deftp Tunable glibc.pthread.mutex_spin_count
> +The @code{glibc.pthread.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
> +@code{PTHREAD_MUTEX_ADAPTIVE_NP} GNU extension.  It affects both
> +@code{pthread_mutex_lock} and @code{pthread_mutex_timedlock}.
> +
> +The spinning is done until either the maximum spin count 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

Ok.

> diff --git a/nptl/Makefile b/nptl/Makefile
> index 49b6faa..284f815 100644
> --- a/nptl/Makefile
> +++ b/nptl/Makefile
> @@ -145,7 +145,7 @@ libpthread-routines = nptl-init nptlfreeres vars events version pt-interp \
>  		      mtx_destroy mtx_init mtx_lock mtx_timedlock \
>  		      mtx_trylock mtx_unlock call_once cnd_broadcast \
>  		      cnd_destroy cnd_init cnd_signal cnd_timedwait cnd_wait \
> -		      tss_create tss_delete tss_get tss_set
> +		      tss_create tss_delete tss_get tss_set pthread_mutex_conf
>  #		      pthread_setuid pthread_seteuid pthread_setreuid \
>  #		      pthread_setresuid \
>  #		      pthread_setgid pthread_setegid pthread_setregid \

Ok.

> diff --git a/nptl/nptl-init.c b/nptl/nptl-init.c
> index 907411d..adf99f1 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.  */
> @@ -431,6 +432,10 @@ __pthread_initialize_minimal_internal (void)
>  
>    /* Determine whether the machine is SMP or not.  */
>    __is_smp = is_smp_system ();
> +
> +#if HAVE_TUNABLES
> +  pthread_tunables_init ();
> +#endif
>  }
>  strong_alias (__pthread_initialize_minimal_internal,
>  	      __pthread_initialize_minimal)

Ok. 

> diff --git a/nptl/pthreadP.h b/nptl/pthreadP.h
> index 19efe1e..9bae78e 100644
> --- a/nptl/pthreadP.h
> +++ b/nptl/pthreadP.h
> @@ -47,12 +47,6 @@
>  #endif
>  
>  
> -/* Adaptive mutex definitions.  */
> -#ifndef MAX_ADAPTIVE_COUNT
> -# define MAX_ADAPTIVE_COUNT 100
> -#endif
> -
> -
>  /* Magic cookie representing robust mutex with dead owner.  */
>  #define PTHREAD_MUTEX_INCONSISTENT	INT_MAX
>  /* Magic cookie representing not recoverable robust mutex.  */
> @@ -188,6 +182,24 @@ enum
>  #define __PTHREAD_COND_SHARED_MASK 1
>  
>  
> +#if HAVE_TUNABLES
> +struct mutex_config
> +{
> +  int spin_count;
> +};
> +
> +extern struct mutex_config __mutex_aconf;
> +#endif
> +
> +/* Adaptive mutex definitions.  */
> +#ifndef MAX_ADAPTIVE_COUNT
> +# if HAVE_TUNABLES
> +#  define MAX_ADAPTIVE_COUNT __mutex_aconf.spin_count
> +# else
> +#  define MAX_ADAPTIVE_COUNT 100
> +# endif
> +#endif
> +
>  /* Internal variables.  */
>  

We try to avoid the logic to check if a define is already define to set a
default value.  If the idea is on future patches to define an arch-specific
value, the preferred strategy is to define the generic and an arch-specific
value in their own headers.

>  
> diff --git a/nptl/pthread_mutex_conf.c b/nptl/pthread_mutex_conf.c
> new file mode 100644
> index 0000000..0da4afe
> --- /dev/null
> +++ b/nptl/pthread_mutex_conf.c
> @@ -0,0 +1,27 @@
> +/* pthread_mutex_conf.c: Pthread mutex tunable parameters.

It is not a rule, but there is no need to duplicate the file name on its
description.

> +   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/>.  */
> +
> +#if HAVE_TUNABLES
> +#include <pthreadP.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,
> +};
> +#endif

If the idea is to keep both non-tunable version and tunable version in sync
when default value change, I would suggest to use an extra define to hold
the '100' value.

Another option, which I think it better, is to avoid make MAX_ADAPTIVE_COUNT
have different meaning depending if tunables is enabled or not and just
create a inline function:

nptl/pthreadP.h:

#define MAX_DEFAULT_ADAPTIVE_COUNT 100

static inline short max_adaptive_count (void)
{
#if HAVE_TUNABLES
  return __mutex_aconf.spin_count;
#else
  return MAX_DEFAULT_ADAPTIVE_COUNT;
#endif
}

And adjust nptl/pthread_mutex_conf.c, nptl/pthread_mutex_lock.c, and
nptl/pthread_mutex_timedlock.c accordingly.

Also, if the idea is to provide a different generic value depending
of the architecture it is a matter to move the MAX_DEFAULT_ADAPTIVE_COUNT
to a generic header and override the header by the architecture.

> diff --git a/nptl/pthread_mutex_conf.h b/nptl/pthread_mutex_conf.h
> new file mode 100644
> index 0000000..97ff98e
> --- /dev/null
> +++ b/nptl/pthread_mutex_conf.h
> @@ -0,0 +1,45 @@
> +/* 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
> +
> +#if HAVE_TUNABLES
> +# define TUNABLE_NAMESPACE pthread
> +# include <stdbool.h>
> +# include <stdint.h>
> +# include <pthreadP.h>
> +# include <pthread_mutex_conf.h>
> +# include <unistd.h>  /* Get STDOUT_FILENO for _dl_printf.  */
> +# include <elf/dl-tunables.h>

Mostly of the includes seems superfluous, I think only pthread_mutex_conf.h
and elf/dl-tunables.h are really required.

> +
> +extern struct mutex_config __mutex_aconf attribute_hidden;
> +
> +static void
> +TUNABLE_CALLBACK (set_mutex_spin_count) (tunable_val_t *valp)
> +{
> +  __mutex_aconf.spin_count = (int32_t) (valp)->numval;
> +}
> +
> +static void pthread_tunables_init (void)
> +{
> +  TUNABLE_GET (mutex_spin_count, int32_t,
> +               TUNABLE_CALLBACK (set_mutex_spin_count));
> +}
> +#endif
> +
> +#endif
> diff --git a/sysdeps/nptl/dl-tunables.list b/sysdeps/nptl/dl-tunables.list
> new file mode 100644
> index 0000000..1cb52e8
> --- /dev/null
> +++ b/sysdeps/nptl/dl-tunables.list
> @@ -0,0 +1,51 @@
> +# 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/>.
> +
> +# Allowed attributes for tunables:
> +#
> +# type: Defaults to STRING
> +# minval: Optional minimum acceptable value
> +# maxval: Optional maximum acceptable value
> +# env_alias: An alias environment variable
> +# security_level: Specify security level of the tunable.  Valid values are:
> +#
> +# 	     SXID_ERASE: (default) Don't read for AT_SECURE binaries and
> +# 	     		 removed so that child processes can't read it.
> +# 	     SXID_IGNORE: Don't read for AT_SECURE binaries, but retained for
> +# 	     		  non-AT_SECURE subprocesses.
> +# 	     NONE: Read all the time.

Do we need to duplicate the same comments from 'elf/dl-tunables.list'?

> +
> +
> +# 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.
> +
> +glibc {
> +  pthread {
> +    mutex_spin_count {
> +      type: INT_32
> +      minval: 0
> +      maxval: 30000
> +      default: 100
> +    }
> +  }
> +}



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