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linux-aio: explain why max batch is checked in laio_io_unplug() 

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>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Message-id: 20220609164712.1539045-3-stefanha@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
This commit is contained in:
Stefan Hajnoczi 2022-06-09 17:47:12 +01:00
parent f387cac5af
commit 99b969fbe1
1 changed files with 6 additions and 0 deletions
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6
block/linux-aio.c
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@ -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))) {