locks: slightly depessimize lockstat

The slow path is always taken when lockstat is enabled. This induces
rdtsc (or other) calls to get the cycle count even when there was no
contention.

Still go to the slow path to not mess with the fast path, but avoid
the heavy lifting unless necessary.

This reduces sys and real time during -j 80 buildkernel:
before: 3651.84s user 1105.59s system 5394% cpu 1:28.18 total
after: 3685.99s user 975.74s system 5450% cpu 1:25.53 total
disabled: 3697.96s user 411.13s system 5261% cpu 1:18.10 total

So note this is still a significant hit.

LOCK_PROFILING results are not affected.

1 files changed, 36 insertions, 25 deletions

diff --git a/sys/kern/kern_rwlock.c b/sys/kern/kern_rwlock.c
index c15e24d07974..9afb756e74d3 100644
--- a/sys/kern/kern_rwlock.c
+++ b/sys/kern/kern_rwlock.c
@@ -438,7 +438,21 @@ __rw_rlock_hard(struct rwlock *rw, struct thread *td, uintptr_t v
 #endif
 #if defined(KDTRACE_HOOKS) || defined(LOCK_PROFILING)
 	uintptr_t state;
-	int doing_lockprof;
+	int doing_lockprof = 0;
+#endif
+
+#ifdef KDTRACE_HOOKS
+	if (LOCKSTAT_PROFILE_ENABLED(rw__acquire)) {
+		if (__rw_rlock_try(rw, td, &v, false LOCK_FILE_LINE_ARG))
+			goto out_lockstat;
+		doing_lockprof = 1;
+		all_time -= lockstat_nsecs(&rw->lock_object);
+		state = v;
+	}
+#endif
+#ifdef LOCK_PROFILING
+	doing_lockprof = 1;
+	state = v;
 #endif
 
 	if (SCHEDULER_STOPPED())
@@ -456,17 +470,6 @@ __rw_rlock_hard(struct rwlock *rw, struct thread *td, uintptr_t v
 	lock_profile_obtain_lock_failed(&rw->lock_object,
 	    &contested, &waittime);
 
-#ifdef LOCK_PROFILING
-	doing_lockprof = 1;
-	state = v;
-#elif defined(KDTRACE_HOOKS)
-	doing_lockprof = lockstat_enabled;
-	if (__predict_false(doing_lockprof)) {
-		all_time -= lockstat_nsecs(&rw->lock_object);
-		state = v;
-	}
-#endif
-
 	for (;;) {
 		if (__rw_rlock_try(rw, td, &v, false LOCK_FILE_LINE_ARG))
 			break;
@@ -615,6 +618,7 @@ retry_ts:
 		LOCKSTAT_RECORD4(rw__spin, rw, all_time - sleep_time,
 		    LOCKSTAT_READER, (state & RW_LOCK_READ) == 0,
 		    (state & RW_LOCK_READ) == 0 ? 0 : RW_READERS(state));
+out_lockstat:
 #endif
 	/*
 	 * TODO: acquire "owner of record" here.  Here be turnstile dragons
@@ -892,10 +896,28 @@ __rw_wlock_hard(volatile uintptr_t *c, uintptr_t v LOCK_FILE_LINE_ARG_DEF)
 #endif
 #if defined(KDTRACE_HOOKS) || defined(LOCK_PROFILING)
 	uintptr_t state;
-	int doing_lockprof;
+	int doing_lockprof = 0;
 #endif
 
 	tid = (uintptr_t)curthread;
+	rw = rwlock2rw(c);
+
+#ifdef KDTRACE_HOOKS
+	if (LOCKSTAT_PROFILE_ENABLED(rw__acquire)) {
+		while (v == RW_UNLOCKED) {
+			if (_rw_write_lock_fetch(rw, &v, tid))
+				goto out_lockstat;
+		}
+		doing_lockprof = 1;
+		all_time -= lockstat_nsecs(&rw->lock_object);
+		state = v;
+	}
+#endif
+#ifdef LOCK_PROFILING
+	doing_lockprof = 1;
+	state = v;
+#endif
+
 	if (SCHEDULER_STOPPED())
 		return;
 
@@ -904,7 +926,6 @@ __rw_wlock_hard(volatile uintptr_t *c, uintptr_t v LOCK_FILE_LINE_ARG_DEF)
 #elif defined(KDTRACE_HOOKS)
 	lock_delay_arg_init(&lda, NULL);
 #endif
-	rw = rwlock2rw(c);
 	if (__predict_false(v == RW_UNLOCKED))
 		v = RW_READ_VALUE(rw);
 
@@ -929,17 +950,6 @@ __rw_wlock_hard(volatile uintptr_t *c, uintptr_t v LOCK_FILE_LINE_ARG_DEF)
 	lock_profile_obtain_lock_failed(&rw->lock_object,
 	    &contested, &waittime);
 
-#ifdef LOCK_PROFILING
-	doing_lockprof = 1;
-	state = v;
-#elif defined(KDTRACE_HOOKS)
-	doing_lockprof = lockstat_enabled;
-	if (__predict_false(doing_lockprof)) {
-		all_time -= lockstat_nsecs(&rw->lock_object);
-		state = v;
-	}
-#endif
-
 	for (;;) {
 		if (v == RW_UNLOCKED) {
 			if (_rw_write_lock_fetch(rw, &v, tid))
@@ -1101,6 +1111,7 @@ retry_ts:
 		LOCKSTAT_RECORD4(rw__spin, rw, all_time - sleep_time,
 		    LOCKSTAT_WRITER, (state & RW_LOCK_READ) == 0,
 		    (state & RW_LOCK_READ) == 0 ? 0 : RW_READERS(state));
+out_lockstat:
 #endif
 	LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(rw__acquire, rw, contested,
 	    waittime, file, line, LOCKSTAT_WRITER);