diff options
Diffstat (limited to 'sysdeps/unix/sysv/linux/s390/elision-lock.c')
| -rw-r--r-- | sysdeps/unix/sysv/linux/s390/elision-lock.c | 30 |
1 files changed, 16 insertions, 14 deletions
diff --git a/sysdeps/unix/sysv/linux/s390/elision-lock.c b/sysdeps/unix/sysv/linux/s390/elision-lock.c index a7c0fccd26..00815375c7 100644 --- a/sysdeps/unix/sysv/linux/s390/elision-lock.c +++ b/sysdeps/unix/sysv/linux/s390/elision-lock.c @@ -50,27 +50,28 @@ __lll_lock_elision (int *futex, short *adapt_count, EXTRAARG int private) 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. - Do not begin a transaction if another cpu has locked the - futex with normal locking. If adapt_count is zero, it remains and the - next pthread_mutex_lock call will try to start a transaction again. */ - if (atomic_load_relaxed (futex) == 0 - && atomic_load_relaxed (adapt_count) <= 0 && aconf.try_tbegin > 0) + 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 (__builtin_expect (status == _HTM_TBEGIN_STARTED, - _HTM_TBEGIN_STARTED)) + 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 some other cpu uses the - lock (writes the futex). */ - if (__builtin_expect (atomic_load_relaxed (futex) == 0, 1)) + 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. */ - if (__builtin_expect (__libc_tx_nesting_depth () <= 1, 1)) + /* 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. */ @@ -118,6 +119,7 @@ __lll_lock_elision (int *futex, short *adapt_count, EXTRAARG int private) } } - /* Use normal locking as fallback path if transaction does not succeed. */ + /* Use normal locking as fallback path if the transaction does not + succeed. */ return LLL_LOCK ((*futex), private); } |