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42bf1c8971
Work around a GCC behavior with hardware transactional memory built-ins. GCC doesn't treat the PowerPC transactional built-ins as compiler barriers, moving instructions past the transaction boundaries and altering their atomicity.
123 lines
3.8 KiB
C
123 lines
3.8 KiB
C
/* elide.h: Generic lock elision support for powerpc.
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Copyright (C) 2015-2016 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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#ifndef ELIDE_PPC_H
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# define ELIDE_PPC_H
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#ifdef ENABLE_LOCK_ELISION
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# include <htm.h>
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# include <elision-conf.h>
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/* Get the new value of adapt_count according to the elision
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configurations. Returns true if the system should retry again or false
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otherwise. */
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static inline bool
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__get_new_count (uint8_t *adapt_count, int attempt)
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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 (_TEXASRU_FAILURE_PERSISTENT (__builtin_get_texasru ()))
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{
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if (__elision_aconf.skip_lock_internal_abort > 0)
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*adapt_count = __elision_aconf.skip_lock_internal_abort;
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return false;
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}
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/* Same logic as above, but for a number of temporary failures in a
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a row. */
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else if (attempt <= 1 && __elision_aconf.skip_lock_out_of_tbegin_retries > 0
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&& __elision_aconf.try_tbegin > 0)
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*adapt_count = __elision_aconf.skip_lock_out_of_tbegin_retries;
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return true;
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}
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/* CONCURRENCY NOTES:
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The evaluation of the macro expression is_lock_free encompasses one or
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more loads from memory locations that are concurrently modified by other
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threads. For lock elision to work, this evaluation and the rest of the
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critical section protected by the lock must be atomic because an
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execution with lock elision must be equivalent to an execution in which
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the lock would have been actually acquired and released. Therefore, we
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evaluate is_lock_free inside of the transaction that represents the
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critical section for which we want to use lock elision, which ensures
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the atomicity that we require. */
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/* Returns 0 if the lock defined by is_lock_free was elided.
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ADAPT_COUNT is a per-lock state variable. */
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# define ELIDE_LOCK(adapt_count, is_lock_free) \
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({ \
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int ret = 0; \
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if (adapt_count > 0) \
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(adapt_count)--; \
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else \
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for (int i = __elision_aconf.try_tbegin; i > 0; i--) \
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{ \
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if (__libc_tbegin (0)) \
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{ \
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if (is_lock_free) \
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{ \
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ret = 1; \
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break; \
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} \
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__libc_tabort (_ABORT_LOCK_BUSY); \
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} \
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else \
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if (!__get_new_count (&adapt_count,i)) \
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break; \
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} \
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ret; \
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})
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# define ELIDE_TRYLOCK(adapt_count, is_lock_free, write) \
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({ \
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int ret = 0; \
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if (__elision_aconf.try_tbegin > 0) \
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{ \
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if (write) \
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__libc_tabort (_ABORT_NESTED_TRYLOCK); \
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ret = ELIDE_LOCK (adapt_count, is_lock_free); \
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} \
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ret; \
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})
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static inline bool
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__elide_unlock (int is_lock_free)
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{
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if (is_lock_free)
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{
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__libc_tend (0);
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return true;
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}
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return false;
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}
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# define ELIDE_UNLOCK(is_lock_free) \
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__elide_unlock (is_lock_free)
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# else
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# define ELIDE_LOCK(adapt_count, is_lock_free) 0
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# define ELIDE_TRYLOCK(adapt_count, is_lock_free, write) 0
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# define ELIDE_UNLOCK(is_lock_free) 0
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#endif /* ENABLE_LOCK_ELISION */
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#endif
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