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

[Adhemerval Zanella <adhemerval.zanella@linaro.org>]

On 04/04/2018 07:25, kemi wrote:
> Hi, Adhemerval
>    Thanks for your review. Could you please help to review the other two patches in this series
> if available? Also, please keep guys in the cc list in case someone may not subscribe glibc 
> mail list. Thanks:)

Yeah, I am checking the patch along with the referenced benchmark on a aarch64
machine as well.  

> 
> See my reply below.
> 
> On 2018年03月30日 15:14, Kemi Wang wrote:
>> On 30/03/2018 04:14, 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.mutex.spin_count tunes can be used by system adminstrator to squeeze
>>> system performance according to different hardware capability and workload
>>> model.
>>>
>>> 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 mutex-conf.c for compilation.
>>>    * nptl/mutex-conf.h: New file.
>>>    * nptl/mutex-conf.c: New file.
>>>
>>> Suggested-by: Andi Kleen <andi.kleen@intel.com>
>>> Signed-off-by: Kemi Wang <kemi.wang@intel.com>
>>
>>> ---
>>>  ChangeLog            | 10 ++++++-
>>>  elf/dl-tunables.list | 10 +++++++
>>>  manual/tunables.texi | 17 ++++++++++++
>>>  nptl/Makefile        |  3 +-
>>>  nptl/mutex-conf.c    | 78 ++++++++++++++++++++++++++++++++++++++++++++++++++++
>>>  nptl/mutex-conf.h    | 31 +++++++++++++++++++++
>>>  6 files changed, 147 insertions(+), 2 deletions(-)
>>>  create mode 100644 nptl/mutex-conf.c
>>>  create mode 100644 nptl/mutex-conf.h
>>>
>>> diff --git a/ChangeLog b/ChangeLog
>>> index 1f98425..472657c 100644
>>> --- a/ChangeLog
>>> +++ b/ChangeLog
>>> @@ -1,5 +1,13 @@
>>> -2018-03-29  Florian Weimer  <fweimer@redhat.com>
>>> +2018-03-30 Kemi Wang <kemi.wang@intel.com>
>>> +
>>> +	* elf/dl-tunables.list: Add glibc.mutex.spin_count entry.
>>> +	* manual/tunables.texi: Add glibc.mutex.spin_count description.
>>> +	* nptl/Makefile: Add mutex-conf.c for compilation.
>>> +	* nptl/mutex-conf.h: New file.
>>> +	* nptl/mutex-conf.c: New file.
>>> +	* nptl/Makefile: Add new file compilation.
>>>  
>>> +2018-03-29  Florian Weimer  <fweimer@redhat.com>
>>>  	* sysdeps/unix/sysv/linux/i386/tst-bz21269.c (do_test): Also
>>>  	capture SIGBUS.
>>>  
>>> diff --git a/elf/dl-tunables.list b/elf/dl-tunables.list
>>> index 1f8ecb8..0c27c14 100644
>>> --- a/elf/dl-tunables.list
>>> +++ b/elf/dl-tunables.list
>>> @@ -121,4 +121,14 @@ glibc {
>>>        default: 3
>>>      }
>>>    }
>>> +
>>> +  mutex {
>>> +	  spin_count {
>>> +		  type: INT_32
>>> +		  minval: 0
>>> +		  maxval: 30000
>>> +		  env_alias: LD_SPIN_COUNT
>>> +		  default: 1000
>>> +	  }
>>> +  }
>>
>> Indentation seems off here, rest the file uses double space while your
>> patch uses tabs.
>>
> 
> Thanks for catching it.
> 
>> Also I not sure if it worth to add environment variable for this tunable,
>> I would rather avoid adding newer ones (and naming seems off, since afaik
>> LD_* meaning some parameters that affects the loader).
>>
> 
> AFAIK, environment variable is what I can think of to give people the possibility of 
> tunes in shell for that, maybe you have better idea?
> 
> Yes, we probably use other name like MUTEX_SPIN_COUNT to avoid confusion, agree?

The tunables framework already provides a environment variable to this [1],
the 'env_alias' is mainly to provide compatibility and to use the same logic
internally.

So I think it is better to use the default tunable env var.

[1] https://www.gnu.org/software/libc/manual/html_node/Tunables.html

> 
>>>  }
>>> diff --git a/manual/tunables.texi b/manual/tunables.texi
>>> index be33c9f..9c6a9f1 100644
>>> --- a/manual/tunables.texi
>>> +++ b/manual/tunables.texi
>>> @@ -281,6 +281,23 @@ 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
>>> +Behavior of ptherad mutex can be tuned to acquire performance improvement
>>> +according to specific hardware capablity and workload character by setting
>>> +the following tunables in the @code{mutex} namespace.
>>> +@end deftp
>>
>> There is a typo (s/ptherad/pthread) 
> 
> thanks for catching it.
> 
>> and I think 'acquire' is not the best
>> word here, I would use 'increase' (I am not a native speaker, so someone
>> might suggest a better wording here).
>>
> 
> All right, I will ask for some native speakers to help check it.
> 
>>> +
>>> +@deftp Tunable glibc.mutex.spin_count
>>> +The @code{glibc.mutex.spin_count} tunable set the maximum times the thread
>>> +should spin on the lock before going to sleep.
>>> +
>>> +The default value of this tunable is @samp{1000}.
>>> +@end deftp
>>
>> I think we need to expand it to specify:
>>
>>   * spinning is only used for the mutex initialized with PTHREAD_MUTEX_ADAPTIVE_NP
>>     GNU extension(current wording is ambiguous).
>>>   * It affects both pthread_mutex_lock and pthread_mutex_timedlock.
>>
>>   * The spinning is done by first issuing an atomic operation similar to trylock
>>     followed by a arch-specific no operation (not sure if we need to expand
>>     how spinning is backoff value is incremented).
>> 	
>       How about this?
>       The spinning is done in case of either the maximum spin count 
>       is reached or lock is acquired during spinning.

It is better for this specific part.

> 
>>   * Not sure 'sleep' is right terminology here, since for Linux 'futex' can
>>     return right away when maximum spin_count it reached.
>>
>     'block' here may be more precise, agree?
>     e.g. use "before calling into the kernel to block" or something like that
> 
>>> +
>>>  @node Hardware Capability Tunables
>>>  @section Hardware Capability Tunables
>>>  @cindex hardware capability tunables
>>> diff --git a/nptl/Makefile b/nptl/Makefile
>>> index 94be92c..5edacea 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 \
>>> +		      mutex-conf
>>>  #		      pthread_setuid pthread_seteuid pthread_setreuid \
>>>  #		      pthread_setresuid \
>>>  #		      pthread_setgid pthread_setegid pthread_setregid \
>>
>> I think a better name for the file would be pthread_mutex_conf.c.
>>
> 
> Agree, will send V2 to fix it.
> 
>>> diff --git a/nptl/mutex-conf.c b/nptl/mutex-conf.c
>>> new file mode 100644
>>> index 0000000..f4ffd6d
>>> --- /dev/null
>>> +++ b/nptl/mutex-conf.c
>>> @@ -0,0 +1,78 @@
>>> +/* mutex-conf.c: Pthread mutex tunable parameters.
>>> +   Copyright (C) 2013-2018 Free Software Foundation, Inc.
>>> +   This file is part of the GNU C Library.
>>> +
>>
>> Copyright should start at 2018 for newer implementations.
>>
> 
> I am not aware of that before, do you mean "Copyright (C) 2018-2023"？

No, just "Copyright (C) 2018".

> 
>>> +   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 <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 times a thread spin on the lock before
>>> +	   * going to sleep */
>>> +	  .spin_count = 1000,
>>> +  };
>>> +
>>
>> Indentation seems off here and in other places in this file.
>>
> 
> Will fix it in V2, thanks for pointing it out.
> 
>>> +#if HAVE_TUNABLES
>>> +#define TUNABLE_CALLBACK_FNDECL(__name, __type)			\
>>
>> Indentation for nested preprocessor is to just one space each level:
>>
>> #if HAVE_TUNABLES
>> # define ... 
>>
>>> +static inline void						\
>>> +__always_inline							\
>>> +do_set_mutex_ ## __name (__type value)			\
>>> +{								\
>>> +  __mutex_aconf.__name = value;				\
>>> +}								\
>>> +void								\
>>> +TUNABLE_CALLBACK (set_mutex_ ## __name) (tunable_val_t *valp) \
>>> +{								\
>>> +  __type value = (__type) (valp)->numval;			\
>>> +  do_set_mutex_ ## __name (value);				\
>>> +}
>>> +
>>> +TUNABLE_CALLBACK_FNDECL (spin_count, int32_t);
>>> +#endif
>>> +
>>> +static void
>>> +mutex_tunables_init (int argc __attribute__ ((unused)),
>>> +			      char **argv  __attribute__ ((unused)),
>>> +					      char **environ)
>>> +{
>>> +#if HAVE_TUNABLES
>>> +
>>> +	TUNABLE_GET (spin_count, int32_t,
>>> +			TUNABLE_CALLBACK (set_mutex_spin_count));
>>> +#endif
>>> +}
>>> +
>>> +#ifdef SHARED
>>> +# define INIT_SECTION ".init_array"
>>> +#else
>>> +# define INIT_SECTION ".preinit_array"
>>> +#endif
>>> +
>>> +void (*const __pthread_mutex_tunables_init_array []) (int, char **, char **)
>>> +  __attribute__ ((section (INIT_SECTION), aligned (sizeof (void *)))) =
>>> +{
>>> +  &mutex_tunables_init
>>> +};> diff --git a/nptl/mutex-conf.h b/nptl/mutex-conf.h
>>> new file mode 100644
>>> index 0000000..babefe3
>>> --- /dev/null
>>> +++ b/nptl/mutex-conf.h
>>> @@ -0,0 +1,31 @@
>>> +/* mutex-conf.h: Pthread mutex tunable parameters.
>>> +   Copyright (C) 2013-2018 Free Software Foundation, Inc.
>>
>> Copyright should start at 2018 for newer implementations.
>>
> 
> Sure.
> 
>>> +   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 _MUTEX_CONF_H
>>> +#define _MUTEX_CONF_H 1
>>> +
>>> +#include <pthread.h>
>>> +#include <time.h>
>>> +
>>> +struct mutex_config
>>> +{
>>> +  int spin_count;
>>> +};
>>> +
>>> +extern struct mutex_config __mutex_aconf attribute_hidden;
>>> +
>>> +#endif
>>>
>>