Date: Fri, 17 Feb 2017 14:55:59 +0000 (UTC) From: Mateusz Guzik <mjg@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r313875 - in head/sys: kern sys Message-ID: <201702171455.v1HEtxS5058649@repo.freebsd.org>
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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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