diff options
| author | Paolo Bonzini <pbonzini@redhat.com> | 2015-12-16 12:32:22 +0100 |
|---|---|---|
| committer | Paolo Bonzini <pbonzini@redhat.com> | 2015-12-17 17:33:49 +0100 |
| commit | f6d153f1bfc7839555309c6e090c6f20c1ce3c0e (patch) | |
| tree | 5599236dbba4c51850a0db71bfa818dbfdfd388f | |
| parent | 3cc8f884996584630734a90c9b3c535af81e3c92 (diff) | |
| download | qemu-f6d153f1bfc7839555309c6e090c6f20c1ce3c0e.zip | |
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 <wency@cn.fujitsu.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <1450265542-4323-1-git-send-email-pbonzini@redhat.com>
| -rw-r--r-- | include/qemu/rcu.h | 6 |
1 files changed, 1 insertions, 5 deletions
diff --git a/include/qemu/rcu.h b/include/qemu/rcu.h index f6d1d56375..7c7cca7f6f 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); } |