1/* Lock elision tunable parameters.
2 Copyright (C) 2014-2024 Free Software Foundation, Inc.
3 This file is part of the GNU C Library.
4
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.
9
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.
14
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/>. */
18
19#include <config.h>
20#include <pthreadP.h>
21#include <elision-conf.h>
22#include <unistd.h>
23#include <dl-procinfo.h>
24
25#define TUNABLE_NAMESPACE elision
26#include <elf/dl-tunables.h>
27
28/* Reasonable initial tuning values, may be revised in the future.
29 This is a conservative initial value. */
30
31struct elision_config __elision_aconf =
32 {
33 /* How often to not attempt to use elision if a transaction aborted
34 because the lock is already acquired. Expressed in number of lock
35 acquisition attempts. */
36 .skip_lock_busy = 3,
37 /* How often to not attempt to use elision if a transaction aborted due
38 to reasons other than other threads' memory accesses. Expressed in
39 number of lock acquisition attempts. */
40 .skip_lock_internal_abort = 3,
41 /* How often to not attempt to use elision if a lock used up all retries
42 without success. Expressed in number of lock acquisition attempts. */
43 .skip_lock_out_of_tbegin_retries = 3,
44 /* How often we try using elision if there is chance for the transaction
45 to finish execution (e.g., it wasn't aborted due to the lock being
46 already acquired. */
47 .try_tbegin = 3,
48 /* Same as SKIP_LOCK_INTERNAL_ABORT but for trylock. */
49 .skip_trylock_internal_abort = 3,
50 };
51
52static inline void
53__always_inline
54do_set_elision_enable (int32_t elision_enable)
55{
56 /* Enable elision if it's available in hardware. It's not necessary to check
57 if __libc_enable_secure isn't enabled since elision_enable will be set
58 according to the default, which is disabled. */
59 if (elision_enable == 1)
60 __pthread_force_elision = (GLRO (dl_hwcap) & HWCAP_S390_TE) ? 1 : 0;
61}
62
63/* The pthread->elision_enable tunable is 0 or 1 indicating that elision
64 should be disabled or enabled respectively. The feature will only be used
65 if it's supported by the hardware. */
66
67void
68TUNABLE_CALLBACK (set_elision_enable) (tunable_val_t *valp)
69{
70 int32_t elision_enable = (int32_t) valp->numval;
71 do_set_elision_enable (elision_enable);
72}
73
74#define TUNABLE_CALLBACK_FNDECL(__name, __type) \
75static inline void \
76__always_inline \
77do_set_elision_ ## __name (__type value) \
78{ \
79 __elision_aconf.__name = value; \
80} \
81void \
82TUNABLE_CALLBACK (set_elision_ ## __name) (tunable_val_t *valp) \
83{ \
84 __type value = (__type) (valp)->numval; \
85 do_set_elision_ ## __name (value); \
86}
87
88TUNABLE_CALLBACK_FNDECL (skip_lock_busy, int32_t);
89TUNABLE_CALLBACK_FNDECL (skip_lock_internal_abort, int32_t);
90TUNABLE_CALLBACK_FNDECL (skip_lock_out_of_tbegin_retries, int32_t);
91TUNABLE_CALLBACK_FNDECL (try_tbegin, int32_t);
92TUNABLE_CALLBACK_FNDECL (skip_trylock_internal_abort, int32_t);
93
94/* Initialize elison. */
95
96void
97__lll_elision_init (void)
98{
99 /* Elision depends on tunables and must be explicitly turned on by setting
100 the appropriate tunable on a supported platform. */
101
102 TUNABLE_GET (enable, int32_t,
103 TUNABLE_CALLBACK (set_elision_enable));
104 TUNABLE_GET (skip_lock_busy, int32_t,
105 TUNABLE_CALLBACK (set_elision_skip_lock_busy));
106 TUNABLE_GET (skip_lock_internal_abort, int32_t,
107 TUNABLE_CALLBACK (set_elision_skip_lock_internal_abort));
108 TUNABLE_GET (skip_lock_after_retries, int32_t,
109 TUNABLE_CALLBACK (set_elision_skip_lock_out_of_tbegin_retries));
110 TUNABLE_GET (tries, int32_t,
111 TUNABLE_CALLBACK (set_elision_try_tbegin));
112 TUNABLE_GET (skip_trylock_internal_abort, int32_t,
113 TUNABLE_CALLBACK (set_elision_skip_trylock_internal_abort));
114
115 if (!__pthread_force_elision)
116 __elision_aconf.try_tbegin = 0; /* Disable elision on rwlocks. */
117}
118

source code of glibc/sysdeps/unix/sysv/linux/s390/elision-conf.c