Re: [PATCH] virtio-blk: support polling I/O

[Suwan Kim <suwan.kim027@gmail.com>]

On Sun, Mar 13, 2022 at 12:42:58PM +0200, Max Gurtovoy wrote:
> 
> On 3/11/2022 5:28 PM, Suwan Kim wrote:
> > This patch supports polling I/O via virtio-blk driver. Polling
> > feature is enabled based on "VIRTIO_BLK_F_MQ" feature and the number
> > of polling queues can be set by QEMU virtio-blk-pci property
> > "num-poll-queues=N". This patch improves the polling I/O throughput
> > and latency.
> > 
> > The virtio-blk driver doesn't not have a poll function and a poll
> > queue and it has been operating in interrupt driven method even if
> > the polling function is called in the upper layer.
> > 
> > virtio-blk polling is implemented upon 'batched completion' of block
> > layer. virtblk_poll() queues completed request to io_comp_batch->req_list
> > and later, virtblk_complete_batch() calls unmap function and ends
> > the requests in batch.
> 
> Maybe we can do the batch in separate commit ?
> 
> For implementing batch in the right way you need to implement .queue_rqs
> call back.
> 
> See NVMe PCI driver implementation.
> 
> If we're here, I would really like to see an implementation of
> blk_mq_ops.timeout callback in virtio-blk.
> 
> I think it will take this driver to the next level.

Thanks for the feedback. I will implement .queue_rqs for virtio-blk
and make a seperate commit. Later, I will try to implement
blk_mq_ops.timeout as you mentioned.

I will send the patch series soon as below.
[1] support .queue_rqs for batch submission
[2] support polling I/O

Regards,
Suwan Kim