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mtx: microoptimize lockstat handling in __mtx_lock_sleep

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This saves a function call and multiple branches after the lock is acquired.
This commit is contained in:
Mateusz Guzik 2017-02-17 14:55:59 +00:00
parent 57abbcd5ad
commit 7640beb920
3 changed files with 11 additions and 6 deletions
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2
sys/kern/kern_lockstat.c
View File

@ -62,7 +62,7 @@ SDT_PROBE_DEFINE1(lockstat, , , sx__downgrade, "struct sx *");
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)

13
sys/kern/kern_mutex.c
View File

@ -446,6 +446,7 @@ __mtx_lock_sleep(volatile uintptr_t *c, uintptr_t v, uintptr_t tid, int opts,
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, uintptr_t v, uintptr_t tid, int opts,
"_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 (;;) {
@ -591,15 +594,17 @@ __mtx_lock_sleep(volatile uintptr_t *c, uintptr_t v, uintptr_t tid, int opts,
#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,
"contention end: %s acquired by %p at %s:%d",
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);

2
sys/sys/lockstat.h
View File

@ -68,7 +68,7 @@ SDT_PROBE_DECLARE(lockstat, , , thread__spin);
#define LOCKSTAT_WRITER 0
#define LOCKSTAT_READER 1
extern int lockstat_enabled;
extern volatile int lockstat_enabled;
#ifdef KDTRACE_HOOKS