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[Qemu-devel] [RFC PATCH 09/13] rcu: avoid repeated system calls
From: |
Paolo Bonzini |
Subject: |
[Qemu-devel] [RFC PATCH 09/13] rcu: avoid repeated system calls |
Date: |
Mon, 15 Aug 2011 14:08:36 -0700 |
Optimization posted to upstream mailing list.
Signed-off-by: Paolo Bonzini <address@hidden>
---
rcu.c | 5 +++++
rcu.h | 22 ++++++++++++----------
2 files changed, 17 insertions(+), 10 deletions(-)
diff --git a/rcu.c b/rcu.c
index e2f347a..aaf53ad 100644
--- a/rcu.c
+++ b/rcu.c
@@ -91,6 +91,11 @@ static void update_counter_and_wait(void)
* while we walk the list.
*/
qemu_event_reset(&rcu_gp_event);
+ QLIST_FOREACH(index, ®istry, node) {
+ ACCESS_ONCE(index->waiting) = true;
+ }
+ __sync_synchronize();
+
QLIST_FOREACH_SAFE(index, ®istry, node, tmp) {
if (!rcu_gp_ongoing(&index->ctr)) {
QLIST_REMOVE(index, node);
diff --git a/rcu.h b/rcu.h
index 86a1fea..96ce9d3 100644
--- a/rcu.h
+++ b/rcu.h
@@ -74,6 +74,8 @@ extern QemuEvent rcu_gp_event;
struct rcu_reader {
/* Data used by both reader and synchronize_rcu() */
unsigned long ctr;
+ bool waiting;
+
/* Data used for registry */
QLIST_ENTRY(rcu_reader) node;
};
@@ -93,24 +95,24 @@ static inline void rcu_quiescent_state(void)
{
smp_mb();
ACCESS_ONCE(rcu_reader.ctr) = ACCESS_ONCE(rcu_gp_ctr);
-#if 0
- /* write rcu_reader.ctr before read futex. Included in
- * qemu_event_set. */
+ /* write rcu_reader.ctr before read waiting. */
smp_mb();
-#endif
- qemu_event_set(&rcu_gp_event);
+ if (ACCESS_ONCE(rcu_reader.waiting)) {
+ ACCESS_ONCE(rcu_reader.waiting) = false;
+ qemu_event_set(&rcu_gp_event);
+ }
}
static inline void rcu_thread_offline(void)
{
smp_mb();
ACCESS_ONCE(rcu_reader.ctr) = 0;
-#if 0
- /* write rcu_reader.ctr before read futex. Included in
- * qemu_event_set. */
+ /* write rcu_reader.ctr before read waiting. */
smp_mb();
-#endif
- qemu_event_set(&rcu_gp_event);
+ if (ACCESS_ONCE(rcu_reader.waiting)) {
+ ACCESS_ONCE(rcu_reader.waiting) = false;
+ qemu_event_set(&rcu_gp_event);
+ }
}
static inline void rcu_thread_online(void)
--
1.7.6
- [Qemu-devel] [RFC PATCH 02/13] rename qemu_event_{init,read}, (continued)
- [Qemu-devel] [RFC PATCH 02/13] rename qemu_event_{init,read}, Paolo Bonzini, 2011/08/15
- [Qemu-devel] [RFC PATCH 03/13] qemu-threads: add QemuEvent, Paolo Bonzini, 2011/08/15
- [Qemu-devel] [RFC PATCH 04/13] qemu-threads: add QemuOnce, Paolo Bonzini, 2011/08/15
- [Qemu-devel] [RFC PATCH 06/13] rcu: add rcutorture, Paolo Bonzini, 2011/08/15
- [Qemu-devel] [RFC PATCH 05/13] add rcu library, Paolo Bonzini, 2011/08/15
- [Qemu-devel] [RFC PATCH 08/13] add call_rcu support, Paolo Bonzini, 2011/08/15
- [Qemu-devel] [RFC PATCH 10/13] rcu: report quiescent states, Paolo Bonzini, 2011/08/15
- [Qemu-devel] [RFC PATCH 11/13] rcuify iohandlers, Paolo Bonzini, 2011/08/15
- [Qemu-devel] [RFC PATCH 09/13] rcu: avoid repeated system calls,
Paolo Bonzini <=
- [Qemu-devel] [RFC PATCH 12/13] split MRU ram list, Paolo Bonzini, 2011/08/15
- [Qemu-devel] [RFC PATCH 07/13] osdep: add qemu_msleep, Paolo Bonzini, 2011/08/15
- [Qemu-devel] [RFC PATCH 13/13] RCUify ram_list, Paolo Bonzini, 2011/08/15