| xf.li | bdd93d5 | 2023-05-12 07:10:14 -0700 | [diff] [blame^] | 1 | /* elide.h: Generic lock elision support. |
| 2 | Copyright (C) 2014-2016 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 | #ifndef ELIDE_H |
| 19 | #define ELIDE_H 1 |
| 20 | |
| 21 | #include <hle.h> |
| 22 | #include <elision-conf.h> |
| 23 | |
| 24 | #define ACCESS_ONCE(x) (* (volatile typeof(x) *) &(x)) |
| 25 | |
| 26 | /* Adapt elision with ADAPT_COUNT and STATUS and decide retries. */ |
| 27 | |
| 28 | static inline bool |
| 29 | elision_adapt(signed char *adapt_count, unsigned int status) |
| 30 | { |
| 31 | if (status & _XABORT_RETRY) |
| 32 | return false; |
| 33 | if ((status & _XABORT_EXPLICIT) |
| 34 | && _XABORT_CODE (status) == _ABORT_LOCK_BUSY) |
| 35 | { |
| 36 | /* Right now we skip here. Better would be to wait a bit |
| 37 | and retry. This likely needs some spinning. Be careful |
| 38 | to avoid writing the lock. */ |
| 39 | if (*adapt_count != __elision_aconf.skip_lock_busy) |
| 40 | ACCESS_ONCE (*adapt_count) = __elision_aconf.skip_lock_busy; |
| 41 | } |
| 42 | /* Internal abort. There is no chance for retry. |
| 43 | Use the normal locking and next time use lock. |
| 44 | Be careful to avoid writing to the lock. */ |
| 45 | else if (*adapt_count != __elision_aconf.skip_lock_internal_abort) |
| 46 | ACCESS_ONCE (*adapt_count) = __elision_aconf.skip_lock_internal_abort; |
| 47 | return true; |
| 48 | } |
| 49 | |
| 50 | /* is_lock_free must be executed inside the transaction */ |
| 51 | |
| 52 | /* Returns true if lock defined by IS_LOCK_FREE was elided. |
| 53 | ADAPT_COUNT is a pointer to per-lock state variable. */ |
| 54 | |
| 55 | #define ELIDE_LOCK(adapt_count, is_lock_free) \ |
| 56 | ({ \ |
| 57 | int ret = 0; \ |
| 58 | \ |
| 59 | if ((adapt_count) <= 0) \ |
| 60 | { \ |
| 61 | for (int i = __elision_aconf.retry_try_xbegin; i > 0; i--) \ |
| 62 | { \ |
| 63 | unsigned int status; \ |
| 64 | if ((status = _xbegin ()) == _XBEGIN_STARTED) \ |
| 65 | { \ |
| 66 | if (is_lock_free) \ |
| 67 | { \ |
| 68 | ret = 1; \ |
| 69 | break; \ |
| 70 | } \ |
| 71 | _xabort (_ABORT_LOCK_BUSY); \ |
| 72 | } \ |
| 73 | if (!elision_adapt (&(adapt_count), status)) \ |
| 74 | break; \ |
| 75 | } \ |
| 76 | } \ |
| 77 | else \ |
| 78 | (adapt_count)--; /* missing updates ok */ \ |
| 79 | ret; \ |
| 80 | }) |
| 81 | |
| 82 | /* Returns true if lock defined by IS_LOCK_FREE was try-elided. |
| 83 | ADAPT_COUNT is a pointer to per-lock state variable. */ |
| 84 | |
| 85 | #define ELIDE_TRYLOCK(adapt_count, is_lock_free, write) ({ \ |
| 86 | int ret = 0; \ |
| 87 | if (__elision_aconf.retry_try_xbegin > 0) \ |
| 88 | { \ |
| 89 | if (write) \ |
| 90 | _xabort (_ABORT_NESTED_TRYLOCK); \ |
| 91 | ret = ELIDE_LOCK (adapt_count, is_lock_free); \ |
| 92 | } \ |
| 93 | ret; \ |
| 94 | }) |
| 95 | |
| 96 | /* Returns true if lock defined by IS_LOCK_FREE was elided. The call |
| 97 | to _xend crashes if the application incorrectly tries to unlock a |
| 98 | lock which has not been locked. */ |
| 99 | |
| 100 | #define ELIDE_UNLOCK(is_lock_free) \ |
| 101 | ({ \ |
| 102 | int ret = 0; \ |
| 103 | if (is_lock_free) \ |
| 104 | { \ |
| 105 | _xend (); \ |
| 106 | ret = 1; \ |
| 107 | } \ |
| 108 | ret; \ |
| 109 | }) |
| 110 | |
| 111 | #endif |