From f6d153f1bfc7839555309c6e090c6f20c1ce3c0e Mon Sep 17 00:00:00 2001 From: Paolo Bonzini Date: Wed, 16 Dec 2015 12:32:22 +0100 Subject: [PATCH] rcu: optimize rcu_read_lock 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. Reviewed-by: Wen Congyang Signed-off-by: Paolo Bonzini Message-Id: <1450265542-4323-1-git-send-email-pbonzini@redhat.com> --- 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); } -- 2.7.4