1/* elision-conf.c: Lock elision tunable parameters.
2 Copyright (C) 2013-2017 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 <http://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/* Reasonable initial tuning values, may be revised in the future.
26 This is a conservative initial value. */
27
28struct elision_config __elision_aconf =
29 {
30 /* How often to not attempt to use elision if a transaction aborted
31 because the lock is already acquired. Expressed in number of lock
32 acquisition attempts. */
33 .skip_lock_busy = 3,
34 /* How often to not attempt to use elision if a transaction aborted due
35 to reasons other than other threads' memory accesses. Expressed in
36 number of lock acquisition attempts. */
37 .skip_lock_internal_abort = 3,
38 /* How often we retry using elision if there is chance for the transaction
39 to finish execution (e.g., it wasn't aborted due to the lock being
40 already acquired. */
41 .retry_try_xbegin = 3,
42 /* Same as SKIP_LOCK_INTERNAL_ABORT but for trylock. */
43 .skip_trylock_internal_abort = 3,
44 };
45
46/* Force elision for all new locks. This is used to decide whether existing
47 DEFAULT locks should be automatically upgraded to elision in
48 pthread_mutex_lock(). Disabled for suid programs. Only used when elision
49 is available. */
50
51int __pthread_force_elision attribute_hidden;
52
53/* Initialize elison. */
54
55static void
56elision_init (int argc __attribute__ ((unused)),
57 char **argv __attribute__ ((unused)),
58 char **environ)
59{
60 int elision_available = HAS_CPU_FEATURE (RTM);
61#ifdef ENABLE_LOCK_ELISION
62 __pthread_force_elision = __libc_enable_secure ? 0 : elision_available;
63#endif
64 if (!elision_available)
65 __elision_aconf.retry_try_xbegin = 0; /* Disable elision on rwlocks */
66}
67
68#ifdef SHARED
69# define INIT_SECTION ".init_array"
70#else
71# define INIT_SECTION ".preinit_array"
72#endif
73
74void (*const __pthread_init_array []) (int, char **, char **)
75 __attribute__ ((section (INIT_SECTION), aligned (sizeof (void *)))) =
76{
77 &elision_init
78};
79