Author: mjg
Date: Fri Feb 17 14:55:59 2017
New Revision: 313875
URL: https://svnweb.freebsd.org/changeset/base/313875
Log:
mtx: microoptimize lockstat handling in __mtx_lock_sleep
This saves a function call and multiple branches after the lock is acquired.
Modified:
head/sys/kern/kern_lockstat.c
head/sys/kern/kern_mutex.c
head/sys/sys/lockstat.h
Modified: head/sys/kern/kern_lockstat.c
==============================================================================
--- head/sys/kern/kern_lockstat.c Fri Feb 17 14:05:57 2017
(r313874)
+++ head/sys/kern/kern_lockstat.c Fri Feb 17 14:55:59 2017
(r313875)
@@ -62,7 +62,7 @@ SDT_PROBE_DEFINE1(lockstat, , , sx__down
SDT_PROBE_DEFINE2(lockstat, , , thread__spin, "struct mtx *", "uint64_t");
-int __read_mostly lockstat_enabled;
+volatile int __read_mostly lockstat_enabled;
uint64_t
lockstat_nsecs(struct lock_object *lo)
Modified: head/sys/kern/kern_mutex.c
==============================================================================
--- head/sys/kern/kern_mutex.c Fri Feb 17 14:05:57 2017 (r313874)
+++ head/sys/kern/kern_mutex.c Fri Feb 17 14:55:59 2017 (r313875)
@@ -446,6 +446,7 @@ __mtx_lock_sleep(volatile uintptr_t *c,
u_int sleep_cnt = 0;
int64_t sleep_time = 0;
int64_t all_time = 0;
+ int doing_lockstat;
#endif
if (SCHEDULER_STOPPED())
@@ -484,7 +485,9 @@ __mtx_lock_sleep(volatile uintptr_t *c,
"_mtx_lock_sleep: %s contested (lock=%p) at %s:%d",
m->lock_object.lo_name, (void *)m->mtx_lock, file, line);
#ifdef KDTRACE_HOOKS
- all_time -= lockstat_nsecs(&m->lock_object);
+ doing_lockstat = lockstat_enabled;
+ if (__predict_false(doing_lockstat))
+ all_time -= lockstat_nsecs(&m->lock_object);
#endif
for (;;) {
@@ -591,9 +594,6 @@ __mtx_lock_sleep(volatile uintptr_t *c,
#endif
v = MTX_READ_VALUE(m);
}
-#ifdef KDTRACE_HOOKS
- all_time += lockstat_nsecs(&m->lock_object);
-#endif
#ifdef KTR
if (cont_logged) {
CTR4(KTR_CONTENTION,
@@ -601,6 +601,11 @@ __mtx_lock_sleep(volatile uintptr_t *c,
m->lock_object.lo_name, (void *)tid, file, line);
}
#endif
+#ifdef KDTRACE_HOOKS
+ if (__predict_true(!doing_lockstat))
+ return;
+ all_time += lockstat_nsecs(&m->lock_object);
+#endif
LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(adaptive__acquire, m, contested,
waittime, file, line);
#ifdef KDTRACE_HOOKS
Modified: head/sys/sys/lockstat.h
==============================================================================
--- head/sys/sys/lockstat.h Fri Feb 17 14:05:57 2017 (r313874)
+++ head/sys/sys/lockstat.h Fri Feb 17 14:55:59 2017 (r313875)
@@ -68,7 +68,7 @@ SDT_PROBE_DECLARE(lockstat, , , thread__
#define LOCKSTAT_WRITER 0
#define LOCKSTAT_READER 1
-extern int lockstat_enabled;
+extern volatile int lockstat_enabled;
#ifdef KDTRACE_HOOKS
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