1 /* elision-conf.c: Lock elision tunable parameters.
2 Copyright (C) 2013-2020 Free Software Foundation, Inc.
3 This file is part of the GNU C Library.
5 The GNU C Library is free software; you can redistribute it and/or
6 modify it under the terms of the GNU Lesser General Public
7 License as published by the Free Software Foundation; either
8 version 2.1 of the License, or (at your option) any later version.
10 The GNU C Library is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 Lesser General Public License for more details.
15 You should have received a copy of the GNU Lesser General Public
16 License along with the GNU C Library; if not, see
17 <https://www.gnu.org/licenses/>. */
21 #include <init-arch.h>
22 #include <elision-conf.h>
26 # define TUNABLE_NAMESPACE elision
28 #include <elf/dl-tunables.h>
30 /* Reasonable initial tuning values, may be revised in the future.
31 This is a conservative initial value. */
33 struct elision_config __elision_aconf
=
35 /* How often to not attempt to use elision if a transaction aborted
36 because the lock is already acquired. Expressed in number of lock
37 acquisition attempts. */
39 /* How often to not attempt to use elision if a transaction aborted due
40 to reasons other than other threads' memory accesses. Expressed in
41 number of lock acquisition attempts. */
42 .skip_lock_internal_abort
= 3,
43 /* How often we retry using elision if there is chance for the transaction
44 to finish execution (e.g., it wasn't aborted due to the lock being
46 .retry_try_xbegin
= 3,
47 /* Same as SKIP_LOCK_INTERNAL_ABORT but for trylock. */
48 .skip_trylock_internal_abort
= 3,
51 /* Force elision for all new locks. This is used to decide whether existing
52 DEFAULT locks should be automatically upgraded to elision in
53 pthread_mutex_lock(). Disabled for suid programs. Only used when elision
56 int __pthread_force_elision attribute_hidden
= 0;
59 static __always_inline
void
60 do_set_elision_enable (int32_t elision_enable
)
62 /* Enable elision if it's avaliable in hardware. It's not necessary to check
63 if __libc_enable_secure isn't enabled since elision_enable will be set
64 according to the default, which is disabled. */
65 if (elision_enable
== 1)
66 __pthread_force_elision
= HAS_CPU_FEATURE (RTM
) ? 1 : 0;
69 /* The pthread->elision_enable tunable is 0 or 1 indicating that elision
70 should be disabled or enabled respectively. The feature will only be used
71 if it's supported by the hardware. */
74 TUNABLE_CALLBACK (set_elision_enable
) (tunable_val_t
*valp
)
76 int32_t elision_enable
= (int32_t) valp
->numval
;
77 do_set_elision_enable (elision_enable
);
80 #define TUNABLE_CALLBACK_FNDECL(__name, __type) \
81 static __always_inline void \
82 do_set_elision_ ## __name (__type value) \
84 __elision_aconf.__name = value; \
87 TUNABLE_CALLBACK (set_elision_ ## __name) (tunable_val_t *valp) \
89 __type value = (__type) (valp)->numval; \
90 do_set_elision_ ## __name (value); \
93 TUNABLE_CALLBACK_FNDECL (skip_lock_busy
, int32_t);
94 TUNABLE_CALLBACK_FNDECL (skip_lock_internal_abort
, int32_t);
95 TUNABLE_CALLBACK_FNDECL (retry_try_xbegin
, int32_t);
96 TUNABLE_CALLBACK_FNDECL (skip_trylock_internal_abort
, int32_t);
99 /* Initialize elision. */
102 elision_init (int argc
__attribute__ ((unused
)),
103 char **argv
__attribute__ ((unused
)),
107 /* Elision depends on tunables and must be explicitly turned on by setting
108 the appropriate tunable on a supported platform. */
110 TUNABLE_GET (enable
, int32_t,
111 TUNABLE_CALLBACK (set_elision_enable
));
112 TUNABLE_GET (skip_lock_busy
, int32_t,
113 TUNABLE_CALLBACK (set_elision_skip_lock_busy
));
114 TUNABLE_GET (skip_lock_internal_abort
, int32_t,
115 TUNABLE_CALLBACK (set_elision_skip_lock_internal_abort
));
116 TUNABLE_GET (tries
, int32_t,
117 TUNABLE_CALLBACK (set_elision_retry_try_xbegin
));
118 TUNABLE_GET (skip_trylock_internal_abort
, int32_t,
119 TUNABLE_CALLBACK (set_elision_skip_trylock_internal_abort
));
122 if (!__pthread_force_elision
)
123 __elision_aconf
.retry_try_xbegin
= 0; /* Disable elision on rwlocks. */
127 # define INIT_SECTION ".init_array"
129 # define INIT_SECTION ".preinit_array"
132 void (*const __pthread_init_array
[]) (int, char **, char **)
133 __attribute__ ((section (INIT_SECTION
), aligned (sizeof (void *)))) =