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

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Message-ID: <9b963af6-0a3f-4957-9227-43673e70b720@nvidia.com>
Date:   Thu, 7 Dec 2023 06:53:59 +0000
From:   Chaitanya Kulkarni <chaitanyak@...dia.com>
To:     Li Feng <fengli@...rtx.com>, 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 12/6/23 20:31, 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>
> ---
>

This patch looks good to me, however I'd update the commit log and add
performance numbers for the non-mq case also, just in-case to show that we
are not breaking non-mq setup.

Being said that, in case we want to be future proof, we can also think of
adding a module param so if someone comes with a scenario where NO_SCHED is
not providing the performance then they can just use the module parameter
instead of again editing the code, irrespective of that :-

Reviewed-by: Chaitanya Kulkarni <kch@...dia.com>

-ck