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Diffstat (limited to 'REORG.TODO/sysdeps/unix/sysv/linux/s390/elision-lock.c')
| -rw-r--r-- | REORG.TODO/sysdeps/unix/sysv/linux/s390/elision-lock.c | 125 |
1 files changed, 125 insertions, 0 deletions
diff --git a/REORG.TODO/sysdeps/unix/sysv/linux/s390/elision-lock.c b/REORG.TODO/sysdeps/unix/sysv/linux/s390/elision-lock.c new file mode 100644 index 0000000000..00815375c7 --- /dev/null +++ b/REORG.TODO/sysdeps/unix/sysv/linux/s390/elision-lock.c @@ -0,0 +1,125 @@ +/* Elided pthread mutex lock. + Copyright (C) 2014-2017 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 <htm.h> +#include <elision-conf.h> +#include <stdint.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 && aconf.try_tbegin > 0) + { + /* Start a transaction and retry it automatically if it aborts with + _HTM_TBEGIN_TRANSIENT. This macro calls tbegin at most retry_cnt + + 1 times. The second argument is considered as retry_cnt. */ + int status = __libc_tbegin_retry ((void *) 0, aconf.try_tbegin - 1); + if (__glibc_likely (status == _HTM_TBEGIN_STARTED)) + { + /* Check the futex to make sure nobody has touched it in the + mean time. This forces the futex into the cache and makes + sure the transaction aborts if another thread acquires the lock + concurrently. */ + if (__glibc_likely (atomic_load_relaxed (futex) == 0)) + /* Lock was free. Return to user code in a transaction. */ + return 0; + + /* Lock was busy. Fall back to normal locking. + This can be the case if e.g. adapt_count was decremented to zero + by a former release and another thread has been waken up and + acquired it. */ + if (__glibc_likely (__libc_tx_nesting_depth () <= 1)) + { + /* In a non-nested transaction there is no need to abort, + which is expensive. Simply end the started transaction. */ + __libc_tend (); + /* Don't try to use transactions for the next couple of times. + See above for why relaxed MO is sufficient. */ + if (aconf.skip_lock_busy > 0) + atomic_store_relaxed (adapt_count, aconf.skip_lock_busy); + } + else /* nesting depth is > 1 */ + { + /* A nested transaction will abort eventually because it + cannot make any progress before *futex changes back to 0. + So we may as well abort immediately. + This persistently aborts the outer transaction to force + the outer mutex use the default lock instead of retrying + with transactions until the try_tbegin of the outer mutex + is zero. + The adapt_count of this inner mutex is not changed, + because using the default lock with the inner mutex + would abort the outer transaction. */ + __libc_tabort (_HTM_FIRST_USER_ABORT_CODE | 1); + __builtin_unreachable (); + } + } + else if (status != _HTM_TBEGIN_TRANSIENT) + { + /* A persistent abort (cc 1 or 3) indicates that a retry is + probably futile. Use the normal locking now and for the + next couple of calls. + Be careful to avoid writing to the lock. See above for why + relaxed MO is sufficient. */ + if (aconf.skip_lock_internal_abort > 0) + atomic_store_relaxed (adapt_count, + aconf.skip_lock_internal_abort); + } + else + { + /* The transaction failed for some retries with + _HTM_TBEGIN_TRANSIENT. Use the normal locking now and for the + next couple of calls. */ + if (aconf.skip_lock_out_of_tbegin_retries > 0) + atomic_store_relaxed (adapt_count, + aconf.skip_lock_out_of_tbegin_retries); + } + } + + /* Use normal locking as fallback path if the transaction does not + succeed. */ + return LLL_LOCK ((*futex), private); +} |