svn commit: r327397 - head/sys/kern
Mateusz Guzik
mjg at FreeBSD.org
Sun Dec 31 00:37:52 UTC 2017
Author: mjg
Date: Sun Dec 31 00:37:50 2017
New Revision: 327397
URL: https://svnweb.freebsd.org/changeset/base/327397
Log:
sx: read the SX_NOADAPTIVE flag and Giant ownership only once
These used to be read multiple times when waiting for the lock the become
free, which had the potential to issue completely avoidable traffic.
Modified:
head/sys/kern/kern_sx.c
Modified: head/sys/kern/kern_sx.c
==============================================================================
--- head/sys/kern/kern_sx.c Sun Dec 31 00:35:11 2017 (r327396)
+++ head/sys/kern/kern_sx.c Sun Dec 31 00:37:50 2017 (r327397)
@@ -91,7 +91,7 @@ PMC_SOFT_DECLARE( , , lock, failed);
WITNESS_SAVE_DECL(Giant) \
#define GIANT_SAVE(work) do { \
- if (mtx_owned(&Giant)) { \
+ if (__predict_false(mtx_owned(&Giant))) { \
work++; \
WITNESS_SAVE(&Giant.lock_object, Giant); \
while (mtx_owned(&Giant)) { \
@@ -533,6 +533,7 @@ _sx_xlock_hard(struct sx *sx, uintptr_t x, int opts LO
#ifdef ADAPTIVE_SX
volatile struct thread *owner;
u_int i, n, spintries = 0;
+ bool adaptive;
#endif
#ifdef LOCK_PROFILING
uint64_t waittime = 0;
@@ -581,6 +582,10 @@ _sx_xlock_hard(struct sx *sx, uintptr_t x, int opts LO
CTR5(KTR_LOCK, "%s: %s contested (lock=%p) at %s:%d", __func__,
sx->lock_object.lo_name, (void *)sx->sx_lock, file, line);
+#ifdef ADAPTIVE_SX
+ adaptive = ((sx->lock_object.lo_flags & SX_NOADAPTIVE) != 0);
+#endif
+
#ifdef HWPMC_HOOKS
PMC_SOFT_CALL( , , lock, failed);
#endif
@@ -597,6 +602,9 @@ _sx_xlock_hard(struct sx *sx, uintptr_t x, int opts LO
state = x;
}
#endif
+#ifndef INVARIANTS
+ GIANT_SAVE(extra_work);
+#endif
for (;;) {
if (x == SX_LOCK_UNLOCKED) {
@@ -604,67 +612,68 @@ _sx_xlock_hard(struct sx *sx, uintptr_t x, int opts LO
break;
continue;
}
+#ifdef INVARIANTS
+ GIANT_SAVE(extra_work);
+#endif
#ifdef KDTRACE_HOOKS
lda.spin_cnt++;
#endif
#ifdef ADAPTIVE_SX
+ if (__predict_false(!adaptive))
+ goto sleepq;
/*
* If the lock is write locked and the owner is
* running on another CPU, spin until the owner stops
* running or the state of the lock changes.
*/
- if ((sx->lock_object.lo_flags & SX_NOADAPTIVE) == 0) {
- if ((x & SX_LOCK_SHARED) == 0) {
- owner = lv_sx_owner(x);
- if (TD_IS_RUNNING(owner)) {
- if (LOCK_LOG_TEST(&sx->lock_object, 0))
- CTR3(KTR_LOCK,
- "%s: spinning on %p held by %p",
- __func__, sx, owner);
- KTR_STATE1(KTR_SCHED, "thread",
- sched_tdname(curthread), "spinning",
- "lockname:\"%s\"",
- sx->lock_object.lo_name);
- GIANT_SAVE(extra_work);
- do {
- lock_delay(&lda);
- x = SX_READ_VALUE(sx);
- owner = lv_sx_owner(x);
- } while (owner != NULL &&
- TD_IS_RUNNING(owner));
- KTR_STATE0(KTR_SCHED, "thread",
- sched_tdname(curthread), "running");
- continue;
- }
- } else if (SX_SHARERS(x) && spintries < asx_retries) {
+ if ((x & SX_LOCK_SHARED) == 0) {
+ owner = lv_sx_owner(x);
+ if (TD_IS_RUNNING(owner)) {
+ if (LOCK_LOG_TEST(&sx->lock_object, 0))
+ CTR3(KTR_LOCK,
+ "%s: spinning on %p held by %p",
+ __func__, sx, owner);
KTR_STATE1(KTR_SCHED, "thread",
sched_tdname(curthread), "spinning",
- "lockname:\"%s\"", sx->lock_object.lo_name);
- GIANT_SAVE(extra_work);
- spintries++;
- for (i = 0; i < asx_loops; i += n) {
- if (LOCK_LOG_TEST(&sx->lock_object, 0))
- CTR4(KTR_LOCK,
- "%s: shared spinning on %p with %u and %u",
- __func__, sx, spintries, i);
- n = SX_SHARERS(x);
- lock_delay_spin(n);
+ "lockname:\"%s\"",
+ sx->lock_object.lo_name);
+ do {
+ lock_delay(&lda);
x = SX_READ_VALUE(sx);
- if ((x & SX_LOCK_SHARED) == 0 ||
- SX_SHARERS(x) == 0)
- break;
- }
-#ifdef KDTRACE_HOOKS
- lda.spin_cnt += i;
-#endif
+ owner = lv_sx_owner(x);
+ } while (owner != NULL &&
+ TD_IS_RUNNING(owner));
KTR_STATE0(KTR_SCHED, "thread",
sched_tdname(curthread), "running");
- if (i != asx_loops)
- continue;
+ continue;
}
+ } else if (SX_SHARERS(x) && spintries < asx_retries) {
+ KTR_STATE1(KTR_SCHED, "thread",
+ sched_tdname(curthread), "spinning",
+ "lockname:\"%s\"", sx->lock_object.lo_name);
+ spintries++;
+ for (i = 0; i < asx_loops; i += n) {
+ if (LOCK_LOG_TEST(&sx->lock_object, 0))
+ CTR4(KTR_LOCK,
+ "%s: shared spinning on %p with %u and %u",
+ __func__, sx, spintries, i);
+ n = SX_SHARERS(x);
+ lock_delay_spin(n);
+ x = SX_READ_VALUE(sx);
+ if ((x & SX_LOCK_SHARED) == 0 ||
+ SX_SHARERS(x) == 0)
+ break;
+ }
+#ifdef KDTRACE_HOOKS
+ lda.spin_cnt += i;
+#endif
+ KTR_STATE0(KTR_SCHED, "thread",
+ sched_tdname(curthread), "running");
+ if (i != asx_loops)
+ continue;
}
#endif
-
+sleepq:
sleepq_lock(&sx->lock_object);
x = SX_READ_VALUE(sx);
retry_sleepq:
@@ -686,8 +695,7 @@ retry_sleepq:
* chain lock. If so, drop the sleep queue lock and try
* again.
*/
- if (!(x & SX_LOCK_SHARED) &&
- (sx->lock_object.lo_flags & SX_NOADAPTIVE) == 0) {
+ if (!(x & SX_LOCK_SHARED) && adaptive) {
owner = (struct thread *)SX_OWNER(x);
if (TD_IS_RUNNING(owner)) {
sleepq_release(&sx->lock_object);
@@ -742,7 +750,6 @@ retry_sleepq:
#ifdef KDTRACE_HOOKS
sleep_time -= lockstat_nsecs(&sx->lock_object);
#endif
- GIANT_SAVE(extra_work);
sleepq_add(&sx->lock_object, NULL, sx->lock_object.lo_name,
SLEEPQ_SX | ((opts & SX_INTERRUPTIBLE) ?
SLEEPQ_INTERRUPTIBLE : 0), SQ_EXCLUSIVE_QUEUE);
@@ -892,6 +899,7 @@ _sx_slock_hard(struct sx *sx, int opts, uintptr_t x LO
GIANT_DECLARE;
#ifdef ADAPTIVE_SX
volatile struct thread *owner;
+ bool adaptive;
#endif
#ifdef LOCK_PROFILING
uint64_t waittime = 0;
@@ -920,6 +928,10 @@ _sx_slock_hard(struct sx *sx, int opts, uintptr_t x LO
lock_delay_arg_init(&lda, NULL);
#endif
+#ifdef ADAPTIVE_SX
+ adaptive = ((sx->lock_object.lo_flags & SX_NOADAPTIVE) != 0);
+#endif
+
#ifdef HWPMC_HOOKS
PMC_SOFT_CALL( , , lock, failed);
#endif
@@ -936,6 +948,9 @@ _sx_slock_hard(struct sx *sx, int opts, uintptr_t x LO
state = x;
}
#endif
+#ifndef INVARIANTS
+ GIANT_SAVE(extra_work);
+#endif
/*
* As with rwlocks, we don't make any attempt to try to block
@@ -944,39 +959,42 @@ _sx_slock_hard(struct sx *sx, int opts, uintptr_t x LO
for (;;) {
if (__sx_slock_try(sx, &x LOCK_FILE_LINE_ARG))
break;
+#ifdef INVARIANTS
+ GIANT_SAVE(extra_work);
+#endif
#ifdef KDTRACE_HOOKS
lda.spin_cnt++;
#endif
#ifdef ADAPTIVE_SX
+ if (__predict_false(!adaptive))
+ goto sleepq;
/*
* If the owner is running on another CPU, spin until
* the owner stops running or the state of the lock
* changes.
*/
- if ((sx->lock_object.lo_flags & SX_NOADAPTIVE) == 0) {
- owner = lv_sx_owner(x);
- if (TD_IS_RUNNING(owner)) {
- if (LOCK_LOG_TEST(&sx->lock_object, 0))
- CTR3(KTR_LOCK,
- "%s: spinning on %p held by %p",
- __func__, sx, owner);
- KTR_STATE1(KTR_SCHED, "thread",
- sched_tdname(curthread), "spinning",
- "lockname:\"%s\"", sx->lock_object.lo_name);
- GIANT_SAVE(extra_work);
- do {
- lock_delay(&lda);
- x = SX_READ_VALUE(sx);
- owner = lv_sx_owner(x);
- } while (owner != NULL && TD_IS_RUNNING(owner));
- KTR_STATE0(KTR_SCHED, "thread",
- sched_tdname(curthread), "running");
- continue;
- }
+ owner = lv_sx_owner(x);
+ if (TD_IS_RUNNING(owner)) {
+ if (LOCK_LOG_TEST(&sx->lock_object, 0))
+ CTR3(KTR_LOCK,
+ "%s: spinning on %p held by %p",
+ __func__, sx, owner);
+ KTR_STATE1(KTR_SCHED, "thread",
+ sched_tdname(curthread), "spinning",
+ "lockname:\"%s\"", sx->lock_object.lo_name);
+ do {
+ lock_delay(&lda);
+ x = SX_READ_VALUE(sx);
+ owner = lv_sx_owner(x);
+ } while (owner != NULL && TD_IS_RUNNING(owner));
+ KTR_STATE0(KTR_SCHED, "thread",
+ sched_tdname(curthread), "running");
+ continue;
}
#endif
+sleepq:
/*
* Some other thread already has an exclusive lock, so
* start the process of blocking.
@@ -999,8 +1017,7 @@ retry_sleepq:
* the owner stops running or the state of the lock
* changes.
*/
- if (!(x & SX_LOCK_SHARED) &&
- (sx->lock_object.lo_flags & SX_NOADAPTIVE) == 0) {
+ if (!(x & SX_LOCK_SHARED) && adaptive) {
owner = (struct thread *)SX_OWNER(x);
if (TD_IS_RUNNING(owner)) {
sleepq_release(&sx->lock_object);
@@ -1035,7 +1052,6 @@ retry_sleepq:
#ifdef KDTRACE_HOOKS
sleep_time -= lockstat_nsecs(&sx->lock_object);
#endif
- GIANT_SAVE(extra_work);
sleepq_add(&sx->lock_object, NULL, sx->lock_object.lo_name,
SLEEPQ_SX | ((opts & SX_INTERRUPTIBLE) ?
SLEEPQ_INTERRUPTIBLE : 0), SQ_SHARED_QUEUE);
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