Avoid entering the slow path of qemu_lockcnt_dec_and_lock if
no bottom half has to be deleted. If a bottom half deletes itself,
it will be picked up on the next visit of the list, or when the
AioContext itself is finalized.
Signed-off-by: Paolo Bonzini <pbonz...@redhat.com>
---
async.c | 13 +++++++++++--
1 file changed, 11 insertions(+), 2 deletions(-)
diff --git a/async.c b/async.c
index 198c53d..1fce3e4 100644
--- a/async.c
+++ b/async.c
@@ -64,19 +64,24 @@ int aio_bh_poll(AioContext *ctx)
{
QEMUBH *bh, **bhp, *next;
int ret;
+ bool deleted = false;
qemu_lockcnt_inc(&ctx->list_lock);
ret = 0;
for (bh = atomic_rcu_read(&ctx->first_bh); bh; bh = next) {
next = atomic_rcu_read(&bh->next);
+ if (bh->deleted) {
+ deleted = true;
+ continue;
+ }
/* The atomic_xchg is paired with the one in qemu_bh_schedule. The
* implicit memory barrier ensures that the callback sees all writes
* done by the scheduling thread. It also ensures that the scheduling
* thread sees the zero before bh->cb has run, and thus will call
* aio_notify again if necessary.
*/
- if (!bh->deleted && atomic_xchg(&bh->scheduled, 0)) {
+ if (atomic_xchg(&bh->scheduled, 0)) {
/* Idle BHs don't count as progress */
if (!bh->idle) {
ret = 1;
@@ -89,6 +94,11 @@ int aio_bh_poll(AioContext *ctx)
}
/* remove deleted bhs */
+ if (!deleted) {
+ qemu_lockcnt_dec(&ctx->list_lock);
+ return ret;
+ }
+
if (qemu_lockcnt_dec_and_lock(&ctx->list_lock)) {
bhp = &ctx->first_bh;
while (*bhp) {
@@ -102,7 +112,6 @@ int aio_bh_poll(AioContext *ctx)
}
qemu_lockcnt_unlock(&ctx->list_lock);
}
-
return ret;
}
--
2.4.3
