On 16/03/2017 17:02, Peter Lieven wrote:commit 3c80ca15 fixed a deadlock scenarion with nested aio_poll invocations.
However, the rescheduling of the completion BH introcuded unnecessary spinning
in the main-loop. On very fast file backends this can even lead to the
"WARNING: I/O thread spun for 1000 iterations" message popping up.
Callgrind reports about 3-4% less instructions with this patch running
qemu-img bench on a ramdisk based VMDK file.
Fixes: 3c80ca158c96ff902a30883a8933e755988948b1
Cc: address@hidden
Signed-off-by: Peter Lieven <address@hidden>
---
util/thread-pool.c | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/util/thread-pool.c b/util/thread-pool.c
index ce6cd30..610646d 100644
--- a/util/thread-pool.c
+++ b/util/thread-pool.c
@@ -188,6 +188,13 @@ restart:
aio_context_release(pool->ctx);
elem->common.cb(elem->common.opaque, elem->ret);
aio_context_acquire(pool->ctx);
+
+ /* We can safely cancel the completion_bh here regardless of someone
+ * else having scheduled it meanwhile because we reenter the
+ * completion function anyway (goto restart).
+ */
+ qemu_bh_cancel(pool->completion_bh);
+
qemu_aio_unref(elem);
goto restart;
} else {
Right, this is the same thing that block/linux-aio.c does.
Okay, so you also think its safe to do this? As far as I have seen you have been working a lot on the aio code recently.
Thanks, Peter |