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 /include | |
| 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 'include')
| -rw-r--r-- | include/qemu/coroutine.h | 5 |
1 files changed, 5 insertions, 0 deletions
diff --git a/include/qemu/coroutine.h b/include/qemu/coroutine.h index fce228f68a..12ce8e109e 100644 --- a/include/qemu/coroutine.h +++ b/include/qemu/coroutine.h @@ -167,6 +167,11 @@ typedef struct CoMutex { */ unsigned locked; + /* Context that is holding the lock. Useful to avoid spinning + * when two coroutines on the same AioContext try to get the lock. :) + */ + AioContext *ctx; + /* A queue of waiters. Elements are added atomically in front of * from_push. to_pop is only populated, and popped from, by whoever * is in charge of the next wakeup. This can be an unlocker or, |