From a3aeb9f09de2d78fa5077b6e8a66d73b7c045a0c Mon Sep 17 00:00:00 2001 From: Peter Lieven Date: Thu, 16 Mar 2017 17:02:49 +0100 Subject: thread-pool: add missing qemu_bh_cancel in completion function 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: qemu-stable@nongnu.org Signed-off-by: Peter Lieven Signed-off-by: Kevin Wolf (cherry picked from commit b7a745dc33a18377bb4a8dfe54d1df01ea60bf66) * drop context dep on b9e413d Signed-off-by: Michael Roth --- thread-pool.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/thread-pool.c b/thread-pool.c index 6fba913529..4157210d16 100644 --- a/thread-pool.c +++ b/thread-pool.c @@ -185,6 +185,13 @@ restart: qemu_bh_schedule(pool->completion_bh); elem->common.cb(elem->common.opaque, elem->ret); + + /* 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 { -- cgit v1.2.1