linux-kernel - Re: [PATCH] virtio_blk: set the default scheduler to none

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Message-ID: <20231225092010-mutt-send-email-mst@kernel.org>
Date: Mon, 25 Dec 2023 09:20:55 -0500
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Li Feng <fengli@...rtx.com>
Cc: Jens Axboe <axboe@...nel.dk>, Jason Wang <jasowang@...hat.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Stefan Hajnoczi <stefanha@...hat.com>,
	Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
	"open list:BLOCK LAYER" <linux-block@...r.kernel.org>,
	open list <linux-kernel@...r.kernel.org>,
	"open list:VIRTIO BLOCK AND SCSI DRIVERS" <virtualization@...ts.linux.dev>
Subject: Re: [PATCH] virtio_blk: set the default scheduler to none

On Thu, Dec 07, 2023 at 12:31:05PM +0800, Li Feng wrote:
> virtio-blk is generally used in cloud computing scenarios, where the
> performance of virtual disks is very important. The mq-deadline scheduler
> has a big performance drop compared to none with single queue. In my tests,
> mq-deadline 4k readread iops were 270k compared to 450k for none. So here
> the default scheduler of virtio-blk is set to "none".
> 
> Signed-off-by: Li Feng <fengli@...rtx.com>

I dropped this for now, pls try to address comments by Christoph/Paolo
if it's still needed

> ---
>  drivers/block/virtio_blk.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> index d53d6aa8ee69..5183ec8e00be 100644
> --- a/drivers/block/virtio_blk.c
> +++ b/drivers/block/virtio_blk.c
> @@ -1367,7 +1367,7 @@ static int virtblk_probe(struct virtio_device *vdev)
>  	vblk->tag_set.ops = &virtio_mq_ops;
>  	vblk->tag_set.queue_depth = queue_depth;
>  	vblk->tag_set.numa_node = NUMA_NO_NODE;
> -	vblk->tag_set.flags = BLK_MQ_F_SHOULD_MERGE;
> +	vblk->tag_set.flags = BLK_MQ_F_SHOULD_MERGE | BLK_MQ_F_NO_SCHED_BY_DEFAULT;
>  	vblk->tag_set.cmd_size =
>  		sizeof(struct virtblk_req) +
>  		sizeof(struct scatterlist) * VIRTIO_BLK_INLINE_SG_CNT;
> -- 
> 2.42.0