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107e6a3c22
Support usable check for all CPU features with the following changes:
1. Change struct cpu_features to
struct cpuid_features
{
struct cpuid_registers cpuid;
struct cpuid_registers usable;
};
struct cpu_features
{
struct cpu_features_basic basic;
struct cpuid_features features[COMMON_CPUID_INDEX_MAX];
unsigned int preferred[PREFERRED_FEATURE_INDEX_MAX];
...
};
so that there is a usable bit for each cpuid bit.
2. After the cpuid bits have been initialized, copy the known bits to the
usable bits. EAX/EBX from INDEX_1 and EAX from INDEX_7 aren't used for
CPU feature detection.
3. Clear the usable bits which require OS support.
4. If the feature is supported by OS, copy its cpuid bit to its usable
bit.
5. Replace HAS_CPU_FEATURE and CPU_FEATURES_CPU_P with CPU_FEATURE_USABLE
and CPU_FEATURE_USABLE_P to check if a feature is usable.
6. Add DEPR_FPU_CS_DS for INDEX_7_EBX_13.
7. Unset MPX feature since it has been deprecated.
The results are
1. If the feature is known and doesn't requre OS support, its usable bit
is copied from the cpuid bit.
2. Otherwise, its usable bit is copied from the cpuid bit only if the
feature is known to supported by OS.
3. CPU_FEATURE_USABLE/CPU_FEATURE_USABLE_P are used to check if the
feature can be used.
4. HAS_CPU_FEATURE/CPU_FEATURE_CPU_P are used to check if CPU supports
the feature.
137 lines
4.7 KiB
C
137 lines
4.7 KiB
C
/* elision-conf.c: Lock elision tunable parameters.
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Copyright (C) 2013-2020 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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<https://www.gnu.org/licenses/>. */
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#include "config.h"
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#include <pthreadP.h>
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#include <init-arch.h>
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#include <elision-conf.h>
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#include <unistd.h>
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#if HAVE_TUNABLES
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# define TUNABLE_NAMESPACE elision
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#endif
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#include <elf/dl-tunables.h>
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/* Reasonable initial tuning values, may be revised in the future.
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This is a conservative initial value. */
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struct elision_config __elision_aconf =
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{
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/* How often to not attempt to use elision if a transaction aborted
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because the lock is already acquired. Expressed in number of lock
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acquisition attempts. */
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.skip_lock_busy = 3,
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/* How often to not attempt to use elision if a transaction aborted due
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to reasons other than other threads' memory accesses. Expressed in
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number of lock acquisition attempts. */
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.skip_lock_internal_abort = 3,
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/* How often we retry using elision if there is chance for the transaction
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to finish execution (e.g., it wasn't aborted due to the lock being
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already acquired. */
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.retry_try_xbegin = 3,
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/* Same as SKIP_LOCK_INTERNAL_ABORT but for trylock. */
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.skip_trylock_internal_abort = 3,
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};
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/* Force elision for all new locks. This is used to decide whether existing
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DEFAULT locks should be automatically upgraded to elision in
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pthread_mutex_lock(). Disabled for suid programs. Only used when elision
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is available. */
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int __pthread_force_elision attribute_hidden = 0;
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#if HAVE_TUNABLES
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static __always_inline void
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do_set_elision_enable (int32_t elision_enable)
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{
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/* Enable elision if it's avaliable in hardware. It's not necessary to check
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if __libc_enable_secure isn't enabled since elision_enable will be set
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according to the default, which is disabled. */
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if (elision_enable == 1)
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__pthread_force_elision = CPU_FEATURE_USABLE (RTM) ? 1 : 0;
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}
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/* The pthread->elision_enable tunable is 0 or 1 indicating that elision
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should be disabled or enabled respectively. The feature will only be used
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if it's supported by the hardware. */
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void
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TUNABLE_CALLBACK (set_elision_enable) (tunable_val_t *valp)
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{
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int32_t elision_enable = (int32_t) valp->numval;
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do_set_elision_enable (elision_enable);
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}
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#define TUNABLE_CALLBACK_FNDECL(__name, __type) \
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static __always_inline void \
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do_set_elision_ ## __name (__type value) \
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{ \
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__elision_aconf.__name = value; \
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} \
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void \
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TUNABLE_CALLBACK (set_elision_ ## __name) (tunable_val_t *valp) \
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{ \
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__type value = (__type) (valp)->numval; \
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do_set_elision_ ## __name (value); \
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}
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TUNABLE_CALLBACK_FNDECL (skip_lock_busy, int32_t);
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TUNABLE_CALLBACK_FNDECL (skip_lock_internal_abort, int32_t);
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TUNABLE_CALLBACK_FNDECL (retry_try_xbegin, int32_t);
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TUNABLE_CALLBACK_FNDECL (skip_trylock_internal_abort, int32_t);
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#endif
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/* Initialize elision. */
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static void
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elision_init (int argc __attribute__ ((unused)),
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char **argv __attribute__ ((unused)),
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char **environ)
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{
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#if HAVE_TUNABLES
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/* Elision depends on tunables and must be explicitly turned on by setting
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the appropriate tunable on a supported platform. */
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TUNABLE_GET (enable, int32_t,
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TUNABLE_CALLBACK (set_elision_enable));
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TUNABLE_GET (skip_lock_busy, int32_t,
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TUNABLE_CALLBACK (set_elision_skip_lock_busy));
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TUNABLE_GET (skip_lock_internal_abort, int32_t,
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TUNABLE_CALLBACK (set_elision_skip_lock_internal_abort));
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TUNABLE_GET (tries, int32_t,
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TUNABLE_CALLBACK (set_elision_retry_try_xbegin));
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TUNABLE_GET (skip_trylock_internal_abort, int32_t,
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TUNABLE_CALLBACK (set_elision_skip_trylock_internal_abort));
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#endif
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if (!__pthread_force_elision)
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__elision_aconf.retry_try_xbegin = 0; /* Disable elision on rwlocks. */
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}
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#ifdef SHARED
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# define INIT_SECTION ".init_array"
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#else
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# define INIT_SECTION ".preinit_array"
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#endif
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void (*const __pthread_init_array []) (int, char **, char **)
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__attribute__ ((section (INIT_SECTION), aligned (sizeof (void *)))) =
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{
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&elision_init
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};
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