Re: [PATCH 2/3] PowerPC: Add adaptive elision to rwlocks

[Adhemerval Zanella <azanella at linux dot vnet dot ibm dot com>]

On 07-11-2014 15:13, Adhemerval Zanella wrote:
> This patch adds support for lock elision using ISA 2.07 hardware
> transactional memory for rwlocks.  The logic is similar to the
> one presented in pthread_mutex lock elision.
>
> --
>
> 	* sysdeps/powerpc/nptl/elide.h: New file: generic lock elision support
> 	for powerpc.
> 	* sysdeps/unix/sysv/linux/powerpc/bits/pthreadtypes.h
> 	[pthread_rwlock_t] (__pad1): Change size to 7 bytes in 64 bits case
> 	and remove it for 32 bits case.
> 	[pthread_rwlock_t] (__rwelision): New field for lock elision.
> 	(__PTHREAD_RWLOCK_ELISION_EXTRA): Adjust for new lock elision field
> 	initialization.
> 	* sysdeps/unix/sysv/linux/powerpc/elision-conf.c (elision_init):
> 	Disable lock elision with rdlocks if elision is not available.
>
> ---
>
> diff --git a/sysdeps/powerpc/nptl/elide.h b/sysdeps/powerpc/nptl/elide.h
> new file mode 100644
> index 0000000..5cc47a3
> --- /dev/null
> +++ b/sysdeps/powerpc/nptl/elide.h
> @@ -0,0 +1,111 @@
> +/* elide.h: Generic lock elision support for powerpc.
> +   Copyright (C) 2014 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 ELIDE_PPC_H
> +# define ELIDE_PPC_H
> +
> +#ifdef ENABLE_LOCK_ELISION
> +# include <htm.h>
> +# include <elision-conf.h>
> +
> +/* Returns true if lock defined by IS_LOCK_FREE was elided.
> +   ADAPT_COUNT is a pointer to per-lock state variable. */
> +
> +static inline bool
> +__elide_lock (uint8_t *adapt_count, int is_lock_free)
> +{
> +  if (*adapt_count > 0)
> +    {
> +      (*adapt_count)--;
> +      return false;
> +    }
> +
> +  for (int i = __elision_aconf.try_tbegin; i > 0; i--)
> +    {
> +      if (__builtin_tbegin (0))
> +	{
> +	  if (is_lock_free)
> +	    return true;
> +	  /* Lock was busy.  */
> +	  __builtin_tabort (_ABORT_LOCK_BUSY);
> +	}
> +      else
> +	{
> +	  /* A persistent failure indicates that a retry will probably
> +	     result in another failure.  Use normal locking now and
> +	     for the next couple of calls.  */
> +	  if (_TEXASRU_FAILURE_PERSISTENT (__builtin_get_texasru ()))
> +	    {
> +	      if (__elision_aconf.skip_lock_internal_abort > 0)
> +		*adapt_count = __elision_aconf.skip_lock_internal_abort;
> +	      break;
> +	    }
> +	  /* Same logic as above, but for for a number of temporary failures in a
> +	     a row.  */
> +	  else if (__elision_aconf.skip_lock_out_of_tbegin_retries > 0
> +		   && __elision_aconf.try_tbegin > 0)
> +	    *adapt_count = __elision_aconf.skip_lock_out_of_tbegin_retries;
> +	}
> +     }
> +
> +  return false;
> +}
> +
> +# define ELIDE_LOCK(adapt_count, is_lock_free) \
> +  __elide_lock (&(adapt_count), is_lock_free)
> +
> +
> +static inline bool
> +__elide_trylock (uint8_t *adapt_count, int is_lock_free, int write)
> +{
> +  if (__elision_aconf.try_tbegin > 0)
> +    {
> +      if (write)
> +	__builtin_tabort (_ABORT_NESTED_TRYLOCK);
> +      return __elide_lock (adapt_count, is_lock_free);
> +    }
> +  return false;
> +}
> +
> +# define ELIDE_TRYLOCK(adapt_count, is_lock_free, write)	\
> +  __elide_trylock (&(adapt_count), is_lock_free, write)
> +
> +
> +static inline bool
> +__elide_unlock (int is_lock_free)
> +{
> +  if (is_lock_free)
> +    {
> +      __builtin_tend (0);
> +      return true;
> +    }
> +  return false;
> +}
> +
> +# define ELIDE_UNLOCK(is_lock_free) \
> +  __elide_unlock (is_lock_free)
> +
> +# else
> +
> +# define ELIDE_LOCK(adapt_count, is_lock_free) 0
> +# define ELIDE_TRYLOCK(adapt_count, is_lock_free, write) 0
> +# define ELIDE_UNLOCK(is_lock_free) 0
> +
> +#endif /* ENABLE_LOCK_ELISION  */
> +
> +#endif
> diff --git a/sysdeps/unix/sysv/linux/powerpc/bits/pthreadtypes.h b/sysdeps/unix/sysv/linux/powerpc/bits/pthreadtypes.h
> index 396a3d9..998f6d4 100644
> --- a/sysdeps/unix/sysv/linux/powerpc/bits/pthreadtypes.h
> +++ b/sysdeps/unix/sysv/linux/powerpc/bits/pthreadtypes.h
> @@ -172,11 +172,13 @@ typedef union
>      unsigned int __nr_writers_queued;
>      int __writer;
>      int __shared;
> -    unsigned long int __pad1;
> +    unsigned char __rwelision;
> +    unsigned char __pad1[7];
>      unsigned long int __pad2;
>      /* FLAGS must stay at this position in the structure to maintain
>         binary compatibility.  */
>      unsigned int __flags;
> +# define __PTHREAD_RWLOCK_ELISION_EXTRA 0, {0, 0, 0, 0, 0, 0, 0 }
>    } __data;
>  # else
>    struct
> @@ -187,20 +189,20 @@ typedef union
>      unsigned int __writer_wakeup;
>      unsigned int __nr_readers_queued;
>      unsigned int __nr_writers_queued;
> -    unsigned char __pad1;
> +    unsigned char __rwelision;
>      unsigned char __pad2;
>      unsigned char __shared;
>      /* FLAGS must stay at this position in the structure to maintain
>         binary compatibility.  */
>      unsigned char __flags;
>      int __writer;
> +#define __PTHREAD_RWLOCK_ELISION_EXTRA 0
>    } __data;
>  # endif
>    char __size[__SIZEOF_PTHREAD_RWLOCK_T];
>    long int __align;
>  } pthread_rwlock_t;
>
> -#define __PTHREAD_RWLOCK_ELISION_EXTRA 0
>
>  typedef union
>  {
> diff --git a/sysdeps/unix/sysv/linux/powerpc/elision-conf.c b/sysdeps/unix/sysv/linux/powerpc/elision-conf.c
> index 60a7900..44833f1 100644
> --- a/sysdeps/unix/sysv/linux/powerpc/elision-conf.c
> +++ b/sysdeps/unix/sysv/linux/powerpc/elision-conf.c
> @@ -64,6 +64,9 @@ elision_init (int argc __attribute__ ((unused)),
>  #ifdef ENABLE_LOCK_ELISION
>    __pthread_force_elision = __libc_enable_secure ? 0 : elision_available;
>  #endif
> +  if (!__pthread_force_elision)
> +    /* Disable elision on rwlocks.  */
> +    __elision_aconf.try_tbegin = 0;
>  }
>
>  #ifdef SHARED
>
Ping.