diff options
| author | Paolo Bonzini <pbonzini@redhat.com> | 2017-02-13 19:12:40 +0100 |
|---|---|---|
| committer | Stefan Hajnoczi <stefanha@redhat.com> | 2017-02-21 11:39:40 +0000 |
| commit | 480cff632221dc4d4889bf72dd0f09cd35096bc1 (patch) | |
| tree | 8fd7a9adcdc981c7785d157d852cded18d4e9034 /util/qemu-coroutine.c | |
| parent | fed20a70e39bb9385020bdc4e8839d95326df8e2 (diff) | |
coroutine-lock: add limited spinning to CoMutex
Running a very small critical section on pthread_mutex_t and CoMutex
shows that pthread_mutex_t is much faster because it doesn't actually
go to sleep. What happens is that the critical section is shorter
than the latency of entering the kernel and thus FUTEX_WAIT always
fails. With CoMutex there is no such latency but you still want to
avoid wait and wakeup. So introduce it artificially.
This only works with one waiters; because CoMutex is fair, it will
always have more waits and wakeups than a pthread_mutex_t.
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Fam Zheng <famz@redhat.com>
Message-id: 20170213181244.16297-3-pbonzini@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Diffstat (limited to 'util/qemu-coroutine.c')
| -rw-r--r-- | util/qemu-coroutine.c | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/util/qemu-coroutine.c b/util/qemu-coroutine.c index 415600dc30..72412e5649 100644 --- a/util/qemu-coroutine.c +++ b/util/qemu-coroutine.c @@ -118,7 +118,7 @@ void qemu_coroutine_enter(Coroutine *co) co->ctx = qemu_get_current_aio_context(); /* Store co->ctx before anything that stores co. Matches - * barrier in aio_co_wake. + * barrier in aio_co_wake and qemu_co_mutex_wake. */ smp_wmb(); |