On Thu, Jun 09, 2022 at 05:47:12PM +0100, Stefan Hajnoczi wrote:
It may not be obvious why laio_io_unplug() checks max batch. I discussed this with Stefano and have added a comment summarizing the reason.Cc: Stefano Garzarella <sgarz...@redhat.com> Cc: Kevin Wolf <kw...@redhat.com> Signed-off-by: Stefan Hajnoczi <stefa...@redhat.com> --- block/linux-aio.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/block/linux-aio.c b/block/linux-aio.c index 6078da7e42..9c2393a2f7 100644 --- a/block/linux-aio.c +++ b/block/linux-aio.c @@ -365,6 +365,12 @@ void laio_io_unplug(BlockDriverState *bs, LinuxAioState *s, assert(s->io_q.plugged); s->io_q.plugged--; + /* + * Why max batch checking is performed here: + * Another BDS may have queued requests with a higher dev_max_batch and + * therefore in_queue could now exceed our dev_max_batch. Re-check the max + * batch so we can honor our device's dev_max_batch. + */ if (s->io_q.in_queue >= laio_max_batch(s, dev_max_batch) || (!s->io_q.plugged && !s->io_q.blocked && !QSIMPLEQ_EMPTY(&s->io_q.pending))) { -- 2.36.1
I should have added that... Reviewed-by: Stefano Garzarella <sgarz...@redhat.com>
