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Subject: Re: [PATCH] virtio_blk: set the default scheduler to none
From: Li Feng <fengli@smartx.com>
In-Reply-To: <20231225092010-mutt-send-email-mst@kernel.org>
Date: Tue, 26 Dec 2023 17:01:40 +0800
Cc: Jens Axboe <axboe@kernel.dk>,
 Jason Wang <jasowang@redhat.com>,
 Paolo Bonzini <pbonzini@redhat.com>,
 Stefan Hajnoczi <stefanha@redhat.com>,
 Xuan Zhuo <xuanzhuo@linux.alibaba.com>,
 "open list:BLOCK LAYER" <linux-block@vger.kernel.org>,
 linux-kernel <linux-kernel@vger.kernel.org>,
 "open list:VIRTIO BLOCK AND SCSI DRIVERS" <virtualization@lists.linux.dev>
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Message-Id: <AB23804D-FF38-47B8-ADC6-C0A19B7083CC@smartx.com>
References: <20231207043118.118158-1-fengli@smartx.com>
 <20231225092010-mutt-send-email-mst@kernel.org>
To: "Michael S. Tsirkin" <mst@redhat.com>

Hi MST and paolo,

mq-deadline is good for slow media, and none is good for high-speed =
media.=20
It depends on how the community views this issue. When virtio-blk adopts
multi-queue,it automatically changes from deadline to none, which is not
uniform here.

I don't have ideas right now to answer Christoph/Paolo's question.

Thanks,
Li

> On Dec 25, 2023, at 22:20, Michael S. Tsirkin <mst@redhat.com> wrote:
>=20
> 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".
>>=20
>> Signed-off-by: Li Feng <fengli@smartx.com>
>=20
> I dropped this for now, pls try to address comments by Christoph/Paolo
> if it's still needed
>=20
>> ---
>> drivers/block/virtio_blk.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>=20
>> 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 =3D &virtio_mq_ops;
>> 	vblk->tag_set.queue_depth =3D queue_depth;
>> 	vblk->tag_set.numa_node =3D NUMA_NO_NODE;
>> -	vblk->tag_set.flags =3D BLK_MQ_F_SHOULD_MERGE;
>> +	vblk->tag_set.flags =3D BLK_MQ_F_SHOULD_MERGE | =
BLK_MQ_F_NO_SCHED_BY_DEFAULT;
>> 	vblk->tag_set.cmd_size =3D
>> 		sizeof(struct virtblk_req) +
>> 		sizeof(struct scatterlist) * VIRTIO_BLK_INLINE_SG_CNT;
>> --=20
>> 2.42.0
>=20