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8d2c0a593b
This patch adds support for lock elision using ISA 2.07 hardware transactional memory instructions for pthread_mutex primitives. Similar to s390 version, the for elision logic defined in 'force-elision.h' is only enabled if ENABLE_LOCK_ELISION is defined. Also, the lock elision code should be able to be built even with a compiler that does not provide HTM support with builtins. However I have noted the performance is sub-optimal due scheduling pressures.
108 lines
3.8 KiB
C
108 lines
3.8 KiB
C
/* elision-lock.c: Elided pthread mutex lock.
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Copyright (C) 2014 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 <stdio.h>
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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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/* PowerISA 2.0.7 Section B.5.5 defines isync to be insufficient as a
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barrier in acquire mechanism for HTM operations, a strong 'sync' is
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required. */
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#undef __arch_compare_and_exchange_val_32_acq
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#define __arch_compare_and_exchange_val_32_acq(mem, newval, oldval) \
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({ \
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__typeof (*(mem)) __tmp; \
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__typeof (mem) __memp = (mem); \
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__asm __volatile ( \
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"1: lwarx %0,0,%1" MUTEX_HINT_ACQ "\n" \
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" cmpw %0,%2\n" \
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" bne 2f\n" \
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" stwcx. %3,0,%1\n" \
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" bne- 1b\n" \
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"2: sync" \
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: "=&r" (__tmp) \
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: "b" (__memp), "r" (oldval), "r" (newval) \
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: "cr0", "memory"); \
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__tmp; \
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})
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#if !defined(LLL_LOCK) && !defined(EXTRAARG)
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/* Make sure the configuration code is always linked in for static
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libraries. */
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#include "elision-conf.c"
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#endif
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#ifndef EXTRAARG
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# define EXTRAARG
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#endif
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#ifndef LLL_LOCK
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# define LLL_LOCK(a,b) lll_lock(a,b), 0
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#endif
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#define aconf __elision_aconf
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/* Adaptive lock using transactions.
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By default the lock region is run as a transaction, and when it
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aborts or the lock is busy the lock adapts itself. */
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int
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__lll_lock_elision (int *lock, short *adapt_count, EXTRAARG int pshared)
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{
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if (*adapt_count > 0)
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{
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(*adapt_count)--;
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goto use_lock;
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}
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int try_begin = aconf.try_tbegin;
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while (1)
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{
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if (__builtin_tbegin (0))
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{
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if (*lock == 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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/* 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 (try_begin-- <= 0
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|| _TEXASRU_FAILURE_PERSISTENT (__builtin_get_texasru ()))
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{
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if (aconf.skip_lock_internal_abort > 0)
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*adapt_count = aconf.skip_lock_internal_abort;
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goto use_lock;
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}
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/* Same logic as above, but for for a number of temporary failures
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in a row. */
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else if (aconf.skip_lock_out_of_tbegin_retries > 0
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&& aconf.try_tbegin > 0)
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*adapt_count = aconf.skip_lock_out_of_tbegin_retries;
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}
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}
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use_lock:
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return LLL_LOCK ((*lock), pshared);
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}
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