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5a414ff7 | 1 | /* Elided pthread mutex lock. |
b168057a | 2 | Copyright (C) 2014-2015 Free Software Foundation, Inc. |
5a414ff7 DV |
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 <pthread.h> | |
20 | #include <pthreadP.h> | |
21 | #include <lowlevellock.h> | |
22 | #include <htmintrin.h> | |
23 | #include <elision-conf.h> | |
24 | #include <stdint.h> | |
25 | ||
26 | #if !defined(LLL_LOCK) && !defined(EXTRAARG) | |
27 | /* Make sure the configuration code is always linked in for static | |
28 | libraries. */ | |
29 | #include "elision-conf.c" | |
30 | #endif | |
31 | ||
32 | #ifndef EXTRAARG | |
33 | #define EXTRAARG | |
34 | #endif | |
35 | #ifndef LLL_LOCK | |
36 | #define LLL_LOCK(a,b) lll_lock(a,b), 0 | |
37 | #endif | |
38 | ||
39 | #define aconf __elision_aconf | |
40 | ||
41 | /* Adaptive lock using transactions. | |
42 | By default the lock region is run as a transaction, and when it | |
43 | aborts or the lock is busy the lock adapts itself. */ | |
44 | ||
45 | int | |
46 | __lll_lock_elision (int *futex, short *adapt_count, EXTRAARG int private) | |
47 | { | |
48 | if (*adapt_count > 0) | |
49 | { | |
50 | /* Lost updates are possible, but harmless. Due to races this might lead | |
51 | to *adapt_count becoming less than zero. */ | |
52 | (*adapt_count)--; | |
53 | goto use_lock; | |
54 | } | |
55 | ||
56 | __asm__ volatile (".machinemode \"zarch_nohighgprs\"\n\t" | |
57 | ".machine \"all\"" | |
58 | : : : "memory"); | |
59 | ||
60 | int try_tbegin; | |
61 | for (try_tbegin = aconf.try_tbegin; | |
62 | try_tbegin > 0; | |
63 | try_tbegin--) | |
64 | { | |
65 | unsigned status; | |
66 | if (__builtin_expect | |
67 | ((status = __builtin_tbegin((void *)0)) == _HTM_TBEGIN_STARTED, 1)) | |
68 | { | |
69 | if (*futex == 0) | |
70 | return 0; | |
71 | /* Lock was busy. Fall back to normal locking. */ | |
72 | if (__builtin_expect (__builtin_tx_nesting_depth (), 1)) | |
73 | { | |
74 | /* In a non-nested transaction there is no need to abort, | |
75 | which is expensive. */ | |
76 | __builtin_tend (); | |
77 | if (aconf.skip_lock_busy > 0) | |
78 | *adapt_count = aconf.skip_lock_busy; | |
79 | goto use_lock; | |
80 | } | |
81 | else /* nesting depth is > 1 */ | |
82 | { | |
83 | /* A nested transaction will abort eventually because it | |
84 | cannot make any progress before *futex changes back to 0. | |
85 | So we may as well abort immediately. | |
86 | This persistently aborts the outer transaction to force | |
87 | the outer mutex use the default lock instead of retrying | |
88 | with transactions until the try_tbegin of the outer mutex | |
89 | is zero. | |
90 | The adapt_count of this inner mutex is not changed, | |
91 | because using the default lock with the inner mutex | |
92 | would abort the outer transaction. | |
93 | */ | |
94 | __builtin_tabort (_HTM_FIRST_USER_ABORT_CODE | 1); | |
95 | } | |
96 | } | |
97 | else | |
98 | { | |
99 | if (status != _HTM_TBEGIN_TRANSIENT) | |
100 | { | |
101 | /* A persistent abort (cc 1 or 3) indicates that a retry is | |
102 | probably futile. Use the normal locking now and for the | |
103 | next couple of calls. | |
104 | Be careful to avoid writing to the lock. */ | |
105 | if (aconf.skip_lock_internal_abort > 0) | |
106 | *adapt_count = aconf.skip_lock_internal_abort; | |
107 | goto use_lock; | |
108 | } | |
109 | } | |
110 | } | |
111 | ||
112 | /* Same logic as above, but for for a number of temporary failures in a | |
113 | row. */ | |
114 | if (aconf.skip_lock_out_of_tbegin_retries > 0 && aconf.try_tbegin > 0) | |
115 | *adapt_count = aconf.skip_lock_out_of_tbegin_retries; | |
116 | ||
117 | use_lock: | |
118 | return LLL_LOCK ((*futex), private); | |
119 | } |