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mtx: pre-read the lock value in thread_lock_flags_

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Since this function is effectively slow path, if we get here the lock is most
likely already taken in which case it is cheaper to not blindly attempt the
atomic op.

While here move hwpmc probe out of the loop to match other primitives.
This commit is contained in:
mjg 2017-12-31 00:33:28 +00:00
parent c5a49cfe43
commit a59af230d8
1 changed files with 9 additions and 7 deletions
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16
sys/kern/kern_mutex.c
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@ -899,6 +899,10 @@ thread_lock_flags_(struct thread *td, int opts, const char *file, int line)
lock_delay_arg_init(&lda, &mtx_spin_delay);
#ifdef HWPMC_HOOKS
PMC_SOFT_CALL( , , lock, failed);
#endif
#ifdef LOCK_PROFILING
doing_lockprof = 1;
#elif defined(KDTRACE_HOOKS)
@ -908,22 +912,20 @@ thread_lock_flags_(struct thread *td, int opts, const char *file, int line)
#endif
for (;;) {
retry:
v = MTX_UNOWNED;
spinlock_enter();
m = td->td_lock;
thread_lock_validate(m, opts, file, line);
v = MTX_READ_VALUE(m);
for (;;) {
if (_mtx_obtain_lock_fetch(m, &v, tid))
break;
if (v == MTX_UNOWNED)
if (v == MTX_UNOWNED) {
if (_mtx_obtain_lock_fetch(m, &v, tid))
break;
continue;
}
if (v == tid) {
m->mtx_recurse++;
break;
}
#ifdef HWPMC_HOOKS
PMC_SOFT_CALL( , , lock, failed);
#endif
lock_profile_obtain_lock_failed(&m->lock_object,
&contested, &waittime);
/* Give interrupts a chance while we spin. */