1 | /* Lock elision tunable parameters. |
2 | Copyright (C) 2014-2022 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 |
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 |
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 |
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 | |