1 /* Lock elision tunable parameters.
2 Copyright (C) 2014-2021 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 #if HAVE_TUNABLES
26 # define TUNABLE_NAMESPACE elision
27 #endif
28 #include <elf/dl-tunables.h>
29
30 /* Reasonable initial tuning values, may be revised in the future.
31 This is a conservative initial value. */
32
33 struct elision_config __elision_aconf =
34 {
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. */
38 .skip_lock_busy = 3,
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 to not attempt to use elision if a lock used up all retries
44 without success. Expressed in number of lock acquisition attempts. */
45 .skip_lock_out_of_tbegin_retries = 3,
46 /* How often we try using elision if there is chance for the transaction
47 to finish execution (e.g., it wasn't aborted due to the lock being
48 already acquired. */
49 .try_tbegin = 3,
50 /* Same as SKIP_LOCK_INTERNAL_ABORT but for trylock. */
51 .skip_trylock_internal_abort = 3,
52 };
53
54 #if HAVE_TUNABLES
55 static inline void
56 __always_inline
do_set_elision_enable(int32_t elision_enable)57 do_set_elision_enable (int32_t elision_enable)
58 {
59 /* Enable elision if it's avaliable in hardware. It's not necessary to check
60 if __libc_enable_secure isn't enabled since elision_enable will be set
61 according to the default, which is disabled. */
62 if (elision_enable == 1)
63 __pthread_force_elision = (GLRO (dl_hwcap) & HWCAP_S390_TE) ? 1 : 0;
64 }
65
66 /* The pthread->elision_enable tunable is 0 or 1 indicating that elision
67 should be disabled or enabled respectively. The feature will only be used
68 if it's supported by the hardware. */
69
70 void
TUNABLE_CALLBACK(set_elision_enable)71 TUNABLE_CALLBACK (set_elision_enable) (tunable_val_t *valp)
72 {
73 int32_t elision_enable = (int32_t) valp->numval;
74 do_set_elision_enable (elision_enable);
75 }
76
77 #define TUNABLE_CALLBACK_FNDECL(__name, __type) \
78 static inline void \
79 __always_inline \
80 do_set_elision_ ## __name (__type value) \
81 { \
82 __elision_aconf.__name = value; \
83 } \
84 void \
85 TUNABLE_CALLBACK (set_elision_ ## __name) (tunable_val_t *valp) \
86 { \
87 __type value = (__type) (valp)->numval; \
88 do_set_elision_ ## __name (value); \
89 }
90
91 TUNABLE_CALLBACK_FNDECL (skip_lock_busy, int32_t);
92 TUNABLE_CALLBACK_FNDECL (skip_lock_internal_abort, int32_t);
93 TUNABLE_CALLBACK_FNDECL (skip_lock_out_of_tbegin_retries, int32_t);
94 TUNABLE_CALLBACK_FNDECL (try_tbegin, int32_t);
95 TUNABLE_CALLBACK_FNDECL (skip_trylock_internal_abort, int32_t);
96 #endif
97
98 /* Initialize elison. */
99
100 void
__lll_elision_init(void)101 __lll_elision_init (void)
102 {
103 #if HAVE_TUNABLES
104 /* Elision depends on tunables and must be explicitly turned on by setting
105 the appropriate tunable on a supported platform. */
106
107 TUNABLE_GET (enable, int32_t,
108 TUNABLE_CALLBACK (set_elision_enable));
109 TUNABLE_GET (skip_lock_busy, int32_t,
110 TUNABLE_CALLBACK (set_elision_skip_lock_busy));
111 TUNABLE_GET (skip_lock_internal_abort, int32_t,
112 TUNABLE_CALLBACK (set_elision_skip_lock_internal_abort));
113 TUNABLE_GET (skip_lock_after_retries, int32_t,
114 TUNABLE_CALLBACK (set_elision_skip_lock_out_of_tbegin_retries));
115 TUNABLE_GET (tries, int32_t,
116 TUNABLE_CALLBACK (set_elision_try_tbegin));
117 TUNABLE_GET (skip_trylock_internal_abort, int32_t,
118 TUNABLE_CALLBACK (set_elision_skip_trylock_internal_abort));
119 #endif
120
121 if (!__pthread_force_elision)
122 __elision_aconf.try_tbegin = 0; /* Disable elision on rwlocks. */
123 }
124