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[Qemu-devel] [PATCH] rcu: optimize rcu_read_lock
From: |
Paolo Bonzini |
Subject: |
[Qemu-devel] [PATCH] rcu: optimize rcu_read_lock |
Date: |
Wed, 16 Dec 2015 12:32:22 +0100 |
rcu_read_lock cannot change rcu_gp_ongoing from true to false
(the previous value of p_rcu_reader->ctr is zero), hence
there is no need to check p_rcu_reader->waiting and wake up
a concurrent synchronize_rcu.
While at it mark the wakeup as unlikely in rcu_read_unlock.
Signed-off-by: Paolo Bonzini <address@hidden>
---
include/qemu/rcu.h | 6 +-----
1 file changed, 1 insertion(+), 5 deletions(-)
diff --git a/include/qemu/rcu.h b/include/qemu/rcu.h
index f6d1d56..7c7cca7 100644
--- a/include/qemu/rcu.h
+++ b/include/qemu/rcu.h
@@ -88,10 +88,6 @@ static inline void rcu_read_lock(void)
ctr = atomic_read(&rcu_gp_ctr);
atomic_xchg(&p_rcu_reader->ctr, ctr);
- if (atomic_read(&p_rcu_reader->waiting)) {
- atomic_set(&p_rcu_reader->waiting, false);
- qemu_event_set(&rcu_gp_event);
- }
}
static inline void rcu_read_unlock(void)
@@ -104,7 +100,7 @@ static inline void rcu_read_unlock(void)
}
atomic_xchg(&p_rcu_reader->ctr, 0);
- if (atomic_read(&p_rcu_reader->waiting)) {
+ if (unlikely(atomic_read(&p_rcu_reader->waiting))) {
atomic_set(&p_rcu_reader->waiting, false);
qemu_event_set(&rcu_gp_event);
}
--
2.5.0
- [Qemu-devel] [PATCH] rcu: optimize rcu_read_lock,
Paolo Bonzini <=