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With TLE enabled, the adapt count variable update incurs an 8% overhead before entering the critical section of an elided mutex. Instead, if it is done right after leaving the critical section, this serialization can be avoided. This alters the existing behavior of __lll_trylock_elision as it will only decrement the adapt_count if it successfully acquires the lock. * sysdeps/unix/sysv/linux/powerpc/elision-lock.c (__lll_lock_elision): Remove adapt_count decrement... * sysdeps/unix/sysv/linux/powerpc/elision-trylock.c (__lll_trylock_elision): Likewise. * sysdeps/unix/sysv/linux/powerpc/elision-unlock.c (__lll_unlock_elision): ... to here. And utilize new adapt_count parameter. * sysdeps/unix/sysv/linux/powerpc/lowlevellock.h (__lll_unlock_elision): Update to include adapt_count parameter. (lll_unlock_elision): Pass pointer to adapt_count variable.
68 lines
2.0 KiB
C
68 lines
2.0 KiB
C
/* elision-trylock.c: Lock eliding trylock for pthreads.
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Copyright (C) 2015 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<http://www.gnu.org/licenses/>. */
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#include <pthread.h>
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#include <pthreadP.h>
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#include <lowlevellock.h>
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#include <elision-conf.h>
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#include "htm.h"
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#define aconf __elision_aconf
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/* Try to elide a futex trylock. FUTEX is the futex variable. ADAPT_COUNT is
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the adaptation counter in the mutex. */
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int
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__lll_trylock_elision (int *futex, short *adapt_count)
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{
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/* Implement POSIX semantics by forbiding nesting elided trylocks. */
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__builtin_tabort (_ABORT_NESTED_TRYLOCK);
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/* Only try a transaction if it's worth it. */
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if (*adapt_count > 0)
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{
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goto use_lock;
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}
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if (__builtin_tbegin (0))
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{
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if (*futex == 0)
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return 0;
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/* Lock was busy. Fall back to normal locking. */
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__builtin_tabort (_ABORT_LOCK_BUSY);
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}
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else
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{
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if (_TEXASRU_FAILURE_PERSISTENT (__builtin_get_texasru ()))
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{
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/* A persistent failure indicates that a retry will probably
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result in another failure. Use normal locking now and
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for the next couple of calls. */
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if (aconf.skip_trylock_internal_abort > 0)
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*adapt_count = aconf.skip_trylock_internal_abort;
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}
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if (aconf.skip_lock_busy > 0)
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*adapt_count = aconf.skip_lock_busy;
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}
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use_lock:
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return lll_trylock (*futex);
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}
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