> Am 16.03.2017 um 17:18 schrieb Paolo Bonzini <[email protected]>: > > > > 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: [email protected] >> Signed-off-by: Peter Lieven <[email protected]> >> --- >> 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
