mirror of
git://sourceware.org/git/glibc.git
synced 2024-12-21 04:31:04 +08:00
120 lines
3.6 KiB
C
120 lines
3.6 KiB
C
/* Elided pthread mutex lock.
|
|
Copyright (C) 2014-2015 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/>. */
|
|
|
|
#include <pthread.h>
|
|
#include <pthreadP.h>
|
|
#include <lowlevellock.h>
|
|
#include <htmintrin.h>
|
|
#include <elision-conf.h>
|
|
#include <stdint.h>
|
|
|
|
#if !defined(LLL_LOCK) && !defined(EXTRAARG)
|
|
/* Make sure the configuration code is always linked in for static
|
|
libraries. */
|
|
#include "elision-conf.c"
|
|
#endif
|
|
|
|
#ifndef EXTRAARG
|
|
#define EXTRAARG
|
|
#endif
|
|
#ifndef LLL_LOCK
|
|
#define LLL_LOCK(a,b) lll_lock(a,b), 0
|
|
#endif
|
|
|
|
#define aconf __elision_aconf
|
|
|
|
/* Adaptive lock using transactions.
|
|
By default the lock region is run as a transaction, and when it
|
|
aborts or the lock is busy the lock adapts itself. */
|
|
|
|
int
|
|
__lll_lock_elision (int *futex, short *adapt_count, EXTRAARG int private)
|
|
{
|
|
if (*adapt_count > 0)
|
|
{
|
|
/* Lost updates are possible, but harmless. Due to races this might lead
|
|
to *adapt_count becoming less than zero. */
|
|
(*adapt_count)--;
|
|
goto use_lock;
|
|
}
|
|
|
|
__asm__ volatile (".machinemode \"zarch_nohighgprs\"\n\t"
|
|
".machine \"all\""
|
|
: : : "memory");
|
|
|
|
int try_tbegin;
|
|
for (try_tbegin = aconf.try_tbegin;
|
|
try_tbegin > 0;
|
|
try_tbegin--)
|
|
{
|
|
unsigned status;
|
|
if (__builtin_expect
|
|
((status = __builtin_tbegin((void *)0)) == _HTM_TBEGIN_STARTED, 1))
|
|
{
|
|
if (*futex == 0)
|
|
return 0;
|
|
/* Lock was busy. Fall back to normal locking. */
|
|
if (__builtin_expect (__builtin_tx_nesting_depth (), 1))
|
|
{
|
|
/* In a non-nested transaction there is no need to abort,
|
|
which is expensive. */
|
|
__builtin_tend ();
|
|
if (aconf.skip_lock_busy > 0)
|
|
*adapt_count = aconf.skip_lock_busy;
|
|
goto use_lock;
|
|
}
|
|
else /* nesting depth is > 1 */
|
|
{
|
|
/* A nested transaction will abort eventually because it
|
|
cannot make any progress before *futex changes back to 0.
|
|
So we may as well abort immediately.
|
|
This persistently aborts the outer transaction to force
|
|
the outer mutex use the default lock instead of retrying
|
|
with transactions until the try_tbegin of the outer mutex
|
|
is zero.
|
|
The adapt_count of this inner mutex is not changed,
|
|
because using the default lock with the inner mutex
|
|
would abort the outer transaction.
|
|
*/
|
|
__builtin_tabort (_HTM_FIRST_USER_ABORT_CODE | 1);
|
|
}
|
|
}
|
|
else
|
|
{
|
|
if (status != _HTM_TBEGIN_TRANSIENT)
|
|
{
|
|
/* A persistent abort (cc 1 or 3) indicates that a retry is
|
|
probably futile. Use the normal locking now and for the
|
|
next couple of calls.
|
|
Be careful to avoid writing to the lock. */
|
|
if (aconf.skip_lock_internal_abort > 0)
|
|
*adapt_count = aconf.skip_lock_internal_abort;
|
|
goto use_lock;
|
|
}
|
|
}
|
|
}
|
|
|
|
/* Same logic as above, but for for a number of temporary failures in a
|
|
row. */
|
|
if (aconf.skip_lock_out_of_tbegin_retries > 0 && aconf.try_tbegin > 0)
|
|
*adapt_count = aconf.skip_lock_out_of_tbegin_retries;
|
|
|
|
use_lock:
|
|
return LLL_LOCK ((*futex), private);
|
|
}
|