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

On Wed, Mar 16, 2022 at 11:33 PM Suwan Kim [off-list ref] wrote:

On Wed, Mar 16, 2022 at 10:02:13AM +0800, Jason Wang wrote:

quoted

On Tue, Mar 15, 2022 at 10:43 PM Suwan Kim [off-list ref] wrote:

quoted

On Tue, Mar 15, 2022 at 04:59:23PM +0800, Jason Wang wrote:

quoted

On Mon, Mar 14, 2022 at 8:33 PM Suwan Kim [off-list ref] wrote:

quoted

On Mon, Mar 14, 2022 at 02:14:53PM +0800, Jason Wang wrote:

quoted

在 2022/3/11 下午11:28, Suwan Kim 写道:

quoted

diff --git a/include/uapi/linux/virtio_blk.h

b/include/uapi/linux/virtio_blk.h

quoted

quoted

index d888f013d9ff..3fcaf937afe1 100644

--- a/include/uapi/linux/virtio_blk.h
+++ b/include/uapi/linux/virtio_blk.h

@@ -119,8 +119,9 @@ struct virtio_blk_config {
     * deallocation of one or more of the sectors.
     */
    __u8 write_zeroes_may_unmap;
+   __u8 unused1;
-   __u8 unused1[3];
+   __virtio16 num_poll_queues;
  } __attribute__((packed));

This looks like a implementation specific (virtio-blk-pci) optimization,

how

quoted

about other implementation like vhost-user-blk?

I didn’t consider vhost-user-blk yet. But does vhost-user-blk also
use vritio_blk_config as kernel-qemu interface?

Yes, but see below.

quoted

Does vhost-user-blk need additional modification to support polling
in kernel side?

No, but the issue is, things like polling looks not a good candidate for
the attributes belonging to the device but the driver. So I have more
questions:

1) what does it really mean for hardware virtio block devices?
2) Does driver polling help for the qemu implementation without polling?
3) Using blk_config means we can only get the benefit from the new device

1) what does it really mean for hardware virtio block devices?
3) Using blk_config means we can only get the benefit from the new device

This patch adds dedicated HW queue for polling purpose to virtio
block device.

So I think it can be a new hw feature. And it can be a new device
that supports hw poll queue.

One possible issue is that the "poll" looks more like a
software/driver concept other than the device/hardware.

quoted

BTW, I have other idea about it.

How about adding “num-poll-queues" property as a driver parameter
like NVMe driver, not to QEMU virtio-blk-pci property?

It should be fine, but we need to listen to others.

To Michael, Stefan, Max

How about using driver parameter instead of virio_blk_config?

I agree.

Thanks

Regards,
Suwan Kim

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