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

Keith Busch
2023-12-08T02:44:40Z

On Fri, Dec 08, 2023 at 10:00:36AM +0800, Ming Lei wrote:
> 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.

More of a curiosity, as I don't immediately even have an HDD to test
with! Isn't it more useful for the host providing the backing HDD use an
appropriate IO scheduler? virtio-blk has similiarities with a stacking
block driver, and we usually don't need to stack IO schedulers.