From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:34030) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Xtakp-0007Ry-Bx for qemu-devel@nongnu.org; Wed, 26 Nov 2014 06:27:32 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Xtakk-0006Pw-Af for qemu-devel@nongnu.org; Wed, 26 Nov 2014 06:27:27 -0500 Received: from mx1.redhat.com ([209.132.183.28]:48579) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Xtakk-0006PS-2a for qemu-devel@nongnu.org; Wed, 26 Nov 2014 06:27:22 -0500 Date: Wed, 26 Nov 2014 12:27:17 +0100 From: Kevin Wolf Message-ID: <20141126112717.GC3548@noname.str.redhat.com> References: <1416900193-3763-1-git-send-email-ming.lei@canonical.com> <1416900193-3763-3-git-send-email-ming.lei@canonical.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1416900193-3763-3-git-send-email-ming.lei@canonical.com> Subject: Re: [Qemu-devel] [PATCH v6 2/3] linux-aio: handling -EAGAIN for !s->io_q.plugged case List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Ming Lei Cc: Paolo Bonzini , qemu-devel@nongnu.org, Stefan Hajnoczi Am 25.11.2014 um 08:23 hat Ming Lei geschrieben: > Previously -EAGAIN is simply ignored for !s->io_q.plugged case, > and sometimes it is easy to cause -EIO to VM, such as NVME device. > > This patch handles -EAGAIN by io queue for !s->io_q.plugged case, > and it will be retried in following aio completion cb. > > Reviewed-by: Paolo Bonzini > Suggested-by: Paolo Bonzini > Signed-off-by: Ming Lei > --- > block/linux-aio.c | 24 ++++++++++++++++-------- > 1 file changed, 16 insertions(+), 8 deletions(-) > > diff --git a/block/linux-aio.c b/block/linux-aio.c > index 11ac828..ac25722 100644 > --- a/block/linux-aio.c > +++ b/block/linux-aio.c > @@ -282,8 +282,13 @@ static int ioq_enqueue(struct qemu_laio_state *s, struct iocb *iocb) > s->io_q.iocbs[idx++] = iocb; > s->io_q.idx = idx; > > - /* submit immediately if queue depth is above 2/3 */ > - if (idx > s->io_q.size * 2 / 3) { > + /* > + * This is reached in two cases: queue not plugged but io_submit > + * returned -EAGAIN, or queue plugged. In the latter case, start > + * submitting some I/O if the queue is getting too full. In the > + * former case, instead, wait until an I/O operation is completed. > + */ Are we guaranteed that an I/O operation is in flight when we get -EAGAIN? The manpage of io_submit isn't very clear on this, "insufficient resources" could be for any reason. Because otherwise we might not ever submit this request. > + if (s->io_q.plugged && unlikely(idx > s->io_q.size * 2 / 3)) { > ioq_submit(s); > } Kevin