Re: [PATCH 2/9] Add the low level infrastructure for pthreads lock elision with TSX

["Carlos O'Donell" <carlos at redhat dot com>]

On 05/10/2013 06:41 PM, Andi Kleen wrote:
> new file mode 100644
> index 0000000..b9a9402
> --- /dev/null
> +++ b/nptl/sysdeps/unix/sysv/linux/x86/elision-conf.h
> @@ -0,0 +1,52 @@
> +/* elision-conf.h: Lock elision tunable parameters.
> +   Copyright (C) 2013 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 _ELISION_CONF_H
> +#define _ELISION_CONF_H 1
> +
> +#include <pthread.h>
> +#include <cpuid.h>
> +#include <time.h>
> +
> +/* Should make sure there is no false sharing on this */
> +
> +struct elision_config
> +{
> +  int retry_lock_busy;
> +  int retry_lock_internal_abort;
> +  int retry_try_xbegin;
> +  int retry_trylock_internal_abort;
> +};
> +
> +extern struct elision_config __elision_aconf attribute_hidden;
> +
> +extern int __rwlock_rtm_enabled;
> +extern int __elision_available;
> +
> +extern int __pthread_mutex_timedlock_nortm (pthread_mutex_t *mutex, const struct timespec *);
> +extern int __pthread_mutex_timedlock_rtm (pthread_mutex_t *mutex, const struct timespec *);
> +extern int __pthread_mutex_timedlock (pthread_mutex_t *mutex, const struct timespec *);
> +extern int __pthread_mutex_lock_nortm (pthread_mutex_t *mutex);
> +extern int __pthread_mutex_lock_rtm (pthread_mutex_t *mutex);
> +extern int __pthread_mutex_lock (pthread_mutex_t *mutex);
> +extern int __pthread_mutex_trylock_nortm (pthread_mutex_t *);
> +extern int __pthread_mutex_trylock_rtm (pthread_mutex_t *);
> +extern int __pthread_mutex_trylock (pthread_mutex_t *);
> +
> +#define SUPPORTS_ELISION 1

Please make this HAVE_ELISION 1. Add a comment explaining it means that
glibc has elision support for mutex and rwlocks.

Convention is either HAVE_*, NEED_* or USE_*.

HAVE_* - You support the feature at compile time.
NEED_* - You need that feature to be enabled at compile time.
USE_* - You have been configured to use this feature (as opposed to another).

For example you would define HAVE_ELISION to 1 to indicate to any other
code that elision support is present.

In generic code that doesn't know if elision is enabled you might write:

#define NEED_ELISION 1
...
#include <elision-conf.h>

To express that you need this support available.

Then in other code which has two distinct paths, one for elision and one
without, you might write:

#if USE_ELISION
/* Code that uses xabort, xbegin, xend ...  */
#else
/* Normal non-elision-aware code.  */
#endif

Cheers,
Carlos.