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Diffstat (limited to 'REORG.TODO/sysdeps/unix/sysv/linux/x86/elision-lock.c')
| -rw-r--r-- | REORG.TODO/sysdeps/unix/sysv/linux/x86/elision-lock.c | 107 |
1 files changed, 107 insertions, 0 deletions
diff --git a/REORG.TODO/sysdeps/unix/sysv/linux/x86/elision-lock.c b/REORG.TODO/sysdeps/unix/sysv/linux/x86/elision-lock.c new file mode 100644 index 0000000000..f5ff111dd3 --- /dev/null +++ b/REORG.TODO/sysdeps/unix/sysv/linux/x86/elision-lock.c @@ -0,0 +1,107 @@ +/* elision-lock.c: Elided pthread mutex lock. + Copyright (C) 2011-2017 Free Software Foundation, Inc. + This file is part of the GNU C Library. + + The GNU C Library is free software; you can redistribute it and/or + modify it under the terms of the GNU Lesser General Public + License as published by the Free Software Foundation; either + version 2.1 of the License, or (at your option) any later version. + + The GNU C Library is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public + License along with the GNU C Library; if not, see + <http://www.gnu.org/licenses/>. */ + +#include <pthread.h> +#include "pthreadP.h" +#include "lowlevellock.h" +#include "hle.h" +#include <elision-conf.h> + +#if !defined(LLL_LOCK) && !defined(EXTRAARG) +/* Make sure the configuration code is always linked in for static + libraries. */ +#include "elision-conf.c" +#endif + +#ifndef EXTRAARG +#define EXTRAARG +#endif +#ifndef LLL_LOCK +#define LLL_LOCK(a,b) lll_lock(a,b), 0 +#endif + +#define aconf __elision_aconf + +/* Adaptive lock using transactions. + By default the lock region is run as a transaction, and when it + aborts or the lock is busy the lock adapts itself. */ + +int +__lll_lock_elision (int *futex, short *adapt_count, EXTRAARG int private) +{ + /* adapt_count can be accessed concurrently; these accesses can be both + inside of transactions (if critical sections are nested and the outer + critical section uses lock elision) and outside of transactions. Thus, + we need to use atomic accesses to avoid data races. However, the + value of adapt_count is just a hint, so relaxed MO accesses are + sufficient. */ + if (atomic_load_relaxed (adapt_count) <= 0) + { + unsigned status; + int try_xbegin; + + for (try_xbegin = aconf.retry_try_xbegin; + try_xbegin > 0; + try_xbegin--) + { + if ((status = _xbegin()) == _XBEGIN_STARTED) + { + if (*futex == 0) + return 0; + + /* Lock was busy. Fall back to normal locking. + Could also _xend here but xabort with 0xff code + is more visible in the profiler. */ + _xabort (_ABORT_LOCK_BUSY); + } + + if (!(status & _XABORT_RETRY)) + { + if ((status & _XABORT_EXPLICIT) + && _XABORT_CODE (status) == _ABORT_LOCK_BUSY) + { + /* Right now we skip here. Better would be to wait a bit + and retry. This likely needs some spinning. See + above for why relaxed MO is sufficient. */ + if (atomic_load_relaxed (adapt_count) + != aconf.skip_lock_busy) + atomic_store_relaxed (adapt_count, aconf.skip_lock_busy); + } + /* Internal abort. There is no chance for retry. + Use the normal locking and next time use lock. + Be careful to avoid writing to the lock. See above for why + relaxed MO is sufficient. */ + else if (atomic_load_relaxed (adapt_count) + != aconf.skip_lock_internal_abort) + atomic_store_relaxed (adapt_count, + aconf.skip_lock_internal_abort); + break; + } + } + } + else + { + /* Use a normal lock until the threshold counter runs out. + Lost updates possible. */ + atomic_store_relaxed (adapt_count, + atomic_load_relaxed (adapt_count) - 1); + } + + /* Use a normal lock here. */ + return LLL_LOCK ((*futex), private); +} |