From: Stefan Hajnoczi <stefanha@redhat.com>
To: Ming Lei <ming.lei@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
Christoph Hellwig <hch@lst.de>,
virtualization@lists.linux-foundation.org,
linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
Jason Wang <jasowang@redhat.com>, Jens Axboe <axboe@kernel.dk>,
slp@redhat.com, sgarzare@redhat.com,
"Michael S. Tsirkin" <mst@redhat.com>
Subject: Re: [PATCH 3/3] virtio_blk: implement blk_mq_ops->poll()
Date: Tue, 25 May 2021 14:20:49 +0100 [thread overview]
Message-ID: <YKz5sQPPNdccztHh@stefanha-x1.localdomain> (raw)
In-Reply-To: <YKypgi2qcYVTgYdv@T590>
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On Tue, May 25, 2021 at 03:38:42PM +0800, Ming Lei wrote:
> On Tue, May 25, 2021 at 09:22:48AM +0200, Paolo Bonzini wrote:
> > On 24/05/21 16:59, Christoph Hellwig wrote:
> > > On Thu, May 20, 2021 at 03:13:05PM +0100, Stefan Hajnoczi wrote:
> > > > Possible drawbacks of this approach:
> > > >
> > > > - Hardware virtio_blk implementations may find virtqueue_disable_cb()
> > > > expensive since it requires DMA. If such devices become popular then
> > > > the virtio_blk driver could use a similar approach to NVMe when
> > > > VIRTIO_F_ACCESS_PLATFORM is detected in the future.
> > > >
> > > > - If a blk_poll() thread is descheduled it not only hurts polling
> > > > performance but also delays completion of non-REQ_HIPRI requests on
> > > > that virtqueue since vq notifications are disabled.
> > >
> > > Yes, I think this is a dangerous configuration. What argument exists
> > > again just using dedicated poll queues?
> >
> > There isn't an equivalent of the admin queue in virtio-blk, which would
> > allow the guest to configure the desired number of poll queues. The number
> > of queues is fixed.
>
> Dedicated vqs can be used for poll only, and I understand VM needn't to know
> if the vq is polled or driven by IRQ in VM.
>
> I tried that in v5.4, but not see obvious IOPS boost, so give up.
>
> https://github.com/ming1/linux/commits/my_v5.4-virtio-irq-poll
Hey, that's cool. I see a lot of similarity between our patches :).
Stefan
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next prev parent reply other threads:[~2021-05-25 13:21 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-20 14:13 [PATCH 0/3] virtio_blk: blk-mq io_poll support Stefan Hajnoczi
2021-05-20 14:13 ` [PATCH 1/3] virtio: add virtioqueue_more_used() Stefan Hajnoczi
2021-05-25 2:23 ` Jason Wang
2021-05-25 8:48 ` Stefan Hajnoczi
2021-05-20 14:13 ` [PATCH 2/3] virtio_blk: avoid repeating vblk->vqs[qid] Stefan Hajnoczi
2021-05-25 2:25 ` Jason Wang
2021-05-20 14:13 ` [PATCH 3/3] virtio_blk: implement blk_mq_ops->poll() Stefan Hajnoczi
2021-05-24 14:59 ` Christoph Hellwig
2021-05-25 7:22 ` Paolo Bonzini
2021-05-25 7:38 ` Ming Lei
2021-05-25 8:06 ` Paolo Bonzini
2021-05-25 13:20 ` Stefan Hajnoczi [this message]
2021-05-25 13:19 ` Stefan Hajnoczi
2021-05-25 3:21 ` Jason Wang
2021-05-25 8:59 ` Stefan Hajnoczi
2021-05-27 5:48 ` Jason Wang
2021-06-03 15:24 ` Stefan Hajnoczi
2021-05-27 2:44 ` Ming Lei
2021-06-03 15:12 ` Stefan Hajnoczi
2021-06-03 15:30 ` [PATCH 0/3] virtio_blk: blk-mq io_poll support Stefan Hajnoczi
2021-06-16 7:43 ` Christoph Hellwig
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