1/* elision-conf.c: Lock elision tunable parameters.
2 Copyright (C) 2013-2023 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 <init-arch.h>
22#include <elision-conf.h>
23#include <unistd.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 we retry using elision if there is chance for the transaction
42 to finish execution (e.g., it wasn't aborted due to the lock being
43 already acquired. */
44 .retry_try_xbegin = 3,
45 /* Same as SKIP_LOCK_INTERNAL_ABORT but for trylock. */
46 .skip_trylock_internal_abort = 3,
47 };
48
49static __always_inline void
50do_set_elision_enable (int32_t elision_enable)
51{
52 /* Enable elision if it's available in hardware. It's not necessary to check
53 if __libc_enable_secure isn't enabled since elision_enable will be set
54 according to the default, which is disabled. */
55 if (elision_enable == 1)
56 __pthread_force_elision = CPU_FEATURE_USABLE (RTM) ? 1 : 0;
57}
58
59/* The pthread->elision_enable tunable is 0 or 1 indicating that elision
60 should be disabled or enabled respectively. The feature will only be used
61 if it's supported by the hardware. */
62
63void
64TUNABLE_CALLBACK (set_elision_enable) (tunable_val_t *valp)
65{
66 int32_t elision_enable = (int32_t) valp->numval;
67 do_set_elision_enable (elision_enable);
68}
69
70#define TUNABLE_CALLBACK_FNDECL(__name, __type) \
71static __always_inline void \
72do_set_elision_ ## __name (__type value) \
73{ \
74 __elision_aconf.__name = value; \
75} \
76void \
77TUNABLE_CALLBACK (set_elision_ ## __name) (tunable_val_t *valp) \
78{ \
79 __type value = (__type) (valp)->numval; \
80 do_set_elision_ ## __name (value); \
81}
82
83TUNABLE_CALLBACK_FNDECL (skip_lock_busy, int32_t);
84TUNABLE_CALLBACK_FNDECL (skip_lock_internal_abort, int32_t);
85TUNABLE_CALLBACK_FNDECL (retry_try_xbegin, int32_t);
86TUNABLE_CALLBACK_FNDECL (skip_trylock_internal_abort, int32_t);
87
88/* Initialize elision. */
89
90void
91__lll_elision_init (void)
92{
93 /* Elision depends on tunables and must be explicitly turned on by setting
94 the appropriate tunable on a supported platform. */
95
96 TUNABLE_GET (enable, int32_t,
97 TUNABLE_CALLBACK (set_elision_enable));
98 TUNABLE_GET (skip_lock_busy, int32_t,
99 TUNABLE_CALLBACK (set_elision_skip_lock_busy));
100 TUNABLE_GET (skip_lock_internal_abort, int32_t,
101 TUNABLE_CALLBACK (set_elision_skip_lock_internal_abort));
102 TUNABLE_GET (tries, int32_t,
103 TUNABLE_CALLBACK (set_elision_retry_try_xbegin));
104 TUNABLE_GET (skip_trylock_internal_abort, int32_t,
105 TUNABLE_CALLBACK (set_elision_skip_trylock_internal_abort));
106
107 if (!__pthread_force_elision)
108 __elision_aconf.retry_try_xbegin = 0; /* Disable elision on rwlocks. */
109}
110