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

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

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.

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).

>  }
> 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) 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).

> +
> +@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).

  * Not sure 'sleep' is right terminology here, since for Linux 'futex' can
    return right away when maximum spin_count it reached.

> +
>  @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.

> 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.

> +   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.

> +#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.

> +   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
>