| Message ID | 20220609164712.1539045-3-stefanha@redhat.com |
|---|---|
| State | New |
| Headers | show |
| Series | linux-aio: fix unbalanced plugged counter in laio_io_unplug() | expand |
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 <sgarzare@redhat.com> >Cc: Kevin Wolf <kwolf@redhat.com> >Signed-off-by: Stefan Hajnoczi <stefanha@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 <sgarzare@redhat.com>
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))) {
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 <sgarzare@redhat.com> Cc: Kevin Wolf <kwolf@redhat.com> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com> --- block/linux-aio.c | 6 ++++++ 1 file changed, 6 insertions(+)