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From: Christoph Hellwig <hch@lst.de>
To: Stefan Hajnoczi <stefanha@redhat.com>
Cc: virtualization@lists.linux-foundation.org,
	linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
	Christoph Hellwig <hch@lst.de>, Jason Wang <jasowang@redhat.com>,
	Paolo Bonzini <pbonzini@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: Mon, 24 May 2021 16:59:28 +0200	[thread overview]
Message-ID: <20210524145928.GA3873@lst.de> (raw)
In-Reply-To: <20210520141305.355961-4-stefanha@redhat.com>

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?

WARNING: multiple messages have this Message-ID (diff)
From: Christoph Hellwig <hch@lst.de>
To: Stefan Hajnoczi <stefanha@redhat.com>
Cc: Jens Axboe <axboe@kernel.dk>,
	"Michael S. Tsirkin" <mst@redhat.com>,
	linux-kernel@vger.kernel.org,
	virtualization@lists.linux-foundation.org,
	linux-block@vger.kernel.org, Paolo Bonzini <pbonzini@redhat.com>,
	Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH 3/3] virtio_blk: implement blk_mq_ops->poll()
Date: Mon, 24 May 2021 16:59:28 +0200	[thread overview]
Message-ID: <20210524145928.GA3873@lst.de> (raw)
In-Reply-To: <20210520141305.355961-4-stefanha@redhat.com>

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?
_______________________________________________
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Virtualization@lists.linux-foundation.org
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  reply	other threads:[~2021-05-24 15:01 UTC|newest]

Thread overview: 42+ 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 ` Stefan Hajnoczi
2021-05-20 14:13 ` [PATCH 1/3] virtio: add virtioqueue_more_used() Stefan Hajnoczi
2021-05-20 14:13   ` Stefan Hajnoczi
2021-05-25  2:23   ` Jason Wang
2021-05-25  2:23     ` Jason Wang
2021-05-25  8:48     ` Stefan Hajnoczi
2021-05-25  8:48       ` Stefan Hajnoczi
2021-05-20 14:13 ` [PATCH 2/3] virtio_blk: avoid repeating vblk->vqs[qid] Stefan Hajnoczi
2021-05-20 14:13   ` Stefan Hajnoczi
2021-05-25  2:25   ` Jason Wang
2021-05-25  2:25     ` Jason Wang
2021-05-20 14:13 ` [PATCH 3/3] virtio_blk: implement blk_mq_ops->poll() Stefan Hajnoczi
2021-05-20 14:13   ` Stefan Hajnoczi
2021-05-24 14:59   ` Christoph Hellwig [this message]
2021-05-24 14:59     ` Christoph Hellwig
2021-05-25  7:22     ` Paolo Bonzini
2021-05-25  7:22       ` Paolo Bonzini
2021-05-25  7:38       ` Ming Lei
2021-05-25  7:38         ` Ming Lei
2021-05-25  8:06         ` Paolo Bonzini
2021-05-25  8:06           ` Paolo Bonzini
2021-05-25 13:20         ` Stefan Hajnoczi
2021-05-25 13:20           ` Stefan Hajnoczi
2021-05-25 13:19     ` Stefan Hajnoczi
2021-05-25 13:19       ` Stefan Hajnoczi
2021-05-25  3:21   ` Jason Wang
2021-05-25  3:21     ` Jason Wang
2021-05-25  8:59     ` Stefan Hajnoczi
2021-05-25  8:59       ` Stefan Hajnoczi
2021-05-27  5:48       ` Jason Wang
2021-05-27  5:48         ` Jason Wang
2021-06-03 15:24         ` Stefan Hajnoczi
2021-06-03 15:24           ` Stefan Hajnoczi
2021-05-27  2:44   ` Ming Lei
2021-05-27  2:44     ` Ming Lei
2021-06-03 15:12     ` Stefan Hajnoczi
2021-06-03 15:12       ` Stefan Hajnoczi
2021-06-03 15:30 ` [PATCH 0/3] virtio_blk: blk-mq io_poll support Stefan Hajnoczi
2021-06-03 15:30   ` Stefan Hajnoczi
2021-06-16  7:43   ` Christoph Hellwig
2021-06-16  7:43     ` Christoph Hellwig

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