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

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Message-ID: <ZXJ4xNawrSRem2qe@fedora>
Date:   Fri, 8 Dec 2023 10:00:36 +0800
From:   Ming Lei <ming.lei@...hat.com>
To:     Li Feng <fengli@...rtx.com>
Cc:     Jens Axboe <axboe@...nel.dk>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        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".

The test result shows you may not test HDD. backing of virtio-blk.

none can lose IO merge capability more or less, so probably sequential IO perf
drops in case of HDD backing.

Thanks,
Ming