linux-kernel - Re: [PATCH 0/3][RFC] virtio-blk: add io_uring passthrough support for virtio-blk

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Message-ID: <0535520b-a6a6-4578-9aca-c698e148004e@linux.alibaba.com>
Date: Tue, 17 Dec 2024 14:08:25 +0800
From: Jingbo Xu <jefflexu@...ux.alibaba.com>
To: Stefan Hajnoczi <stefanha@...il.com>,
 Christoph Hellwig <hch@...radead.org>, Jens Axboe <axboe@...nel.dk>
Cc: Ferry Meng <mengferry@...ux.alibaba.com>,
 "Michael S . Tsirkin" <mst@...hat.com>, Jason Wang <jasowang@...hat.com>,
 linux-block@...r.kernel.org, virtualization@...ts.linux.dev,
 linux-kernel@...r.kernel.org, io-uring@...r.kernel.org,
 Joseph Qi <joseph.qi@...ux.alibaba.com>
Subject: Re: [PATCH 0/3][RFC] virtio-blk: add io_uring passthrough support for
 virtio-blk

Hi Stefan & Christoph,

On 12/17/24 12:13 AM, Stefan Hajnoczi wrote:
> On Mon, 16 Dec 2024 at 10:54, Christoph Hellwig <hch@...radead.org> wrote:
>>
>> Hacking passthrough into virtio_blk seems like not very good layering.
>> If you have a use case where you want to use the core kernel virtio code
>> but not the protocol drivers we'll probably need a virtqueue passthrough
>> option of some kind.
> 
> I think people are finding that submitting I/O via uring_cmd is faster
> than traditional io_uring. The use case isn't really passthrough, it's
> bypass :).

Right, the initial purpose is bypassing the block layer (in the guest)
to achieve better latency when the user process is operating on a raw
virtio-blk device directly.

> 
> That's why I asked Jens to weigh in on whether there is a generic
> block layer solution here. If uring_cmd is faster then maybe a generic
> uring_cmd I/O interface can be defined without tying applications to
> device-specific commands. Or maybe the traditional io_uring code path
> can be optimized so that bypass is no longer attractive.

We are fine with that if it looks good to Jens.

-- 
Thanks,
Jingbo