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


Carlos, thanks for your comments:)

On 2018/11/28 上午4:51, Carlos O'Donell wrote:
> On 11/27/18 12:01 AM, kemi wrote:
>> +Carlos
> 
> Are there any outstanding comments regarding this code? You've seen a lot
> of reviews and I have not double checked that outstanding comments do not
> remain from v1->v9.
> 

I believe I have tried my best to address the comments from community.
And for each reviewer, I have answered their questions in the emails.

> My own comments are below. I think if you address those we're ready to
> commit these changes. I would like to see us move on more of these kinds
> of tunables which expose previously uncontrollable options for specific
> workloads. Defaults should still be useful, and I'd like to hear your input
> on wether you think 100 is a useful defaul.
> 

The best spin count number should be architecture-specific. E.g. the pause in Skylake
is 10x expensive than before. 

In this patch, we don't have any functionality change, using previous default number 100,
though may not be the best, it will not trigger performance regression at least. 

we have discussed this issue before:
https://sourceware.org/ml/libc-alpha/2018-05/msg00545.html

> Please post v10. Thank you!
> 

sure

>> On 2018/11/27 上午10:43, kemi wrote:
>>> PING~
>>>
>>> On 2018/11/22 上午9:45, 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 ().
>>>>
>>>> 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
> 
> OK.
> 
>>>>  * 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
> 
> s/of POSIX thread/of POSIX threads/g
> 

OK

>>>> +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}.
> 
> OK.
> 
>>>> +
>>>> +The spinning is done until either the maximum spin count is reached or
> 
> s/The spinning is done/The thread spins/g
> 

OK

>>>> +the lock is acquired.
> 
> OK.
> 
>>>> +
>>>> +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 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
> 
> OK.
> 
>>>>  #		      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 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>
> 
> OK.
> 
>>>>  
>>>>  #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
> 
> OK.
> 
>>>>  }
>>>>  strong_alias (__pthread_initialize_minimal_internal,
>>>>  	      __pthread_initialize_minimal)
>>>> 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;
>>>> +};
> 
> OK.
> 
>>>> +
>>>> +extern struct mutex_config __mutex_aconf;
> 
> OK.
> 
>>>> +#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
> 
> Please define a DEFAULT_ADAPTIVE_COUNT to 100 and use it later
> in pthread_mutex_conf.c.
> 
> Please add a comment to DEFAULT_ADAPTIVE_COUNT, since you
> touched the code we should comment it a bit more:
> 
> /* The choice of 100 spins for the default spin count for
>    an adaptive spin is a completely arbitrary choice that
>    has not been evaluated thoroughly using modern hardware.  */
> 

Will do it.

>>>> +# endif
>>>> +#endif
>>>> +
>>>>  /* Internal variables.  */
>>>>  
>>>>  
>>>> 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.
> 
> Use just "pthread mutex tunable parameters."
> 

OK

>>>> +   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,
> 
> Should use DEFAULT_ADAPTIVE_COUNT instead of repeating the 100.
> 

OK

>>>> +};
>>>> +#endif
>>>> 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.
> 
> Use just "pthread mutex tunable parameters."
> 

OK

>>>> +   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>
>>>> +
>>>> +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
> 
> OK.
> 
>>>> 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.
>>>> +
>>>> +
>>>> +# 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
>>>> +    }
>>>> +  }
>>>> +}
>>>>
> 
> I don't like the duplication of DEFAULT_ADAPTIVE_MAX here,
> similarly all the other duplicated parameters in glibc.elision
> namespace, but I don't think we can do better without a lot
> more work to allow macro expansion.
> 
> OK.
>  let's just keep the magic number 100 here?


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