Re: [RFC v4 00/11] blkio: add libblkio BlockDriver

[Stefan Hajnoczi <stefanha@redhat.com>]

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On Tue, Aug 23, 2022 at 08:31:03PM +0300, Vladimir Sementsov-Ogievskiy wrote:
> On 8/23/22 01:23, Stefan Hajnoczi wrote:
> > The remainder of the patch series reworks the existing QEMU bdrv_register_buf()
> > API so virtio-blk emulation efficiently map guest RAM for libblkio - some
> > libblkio drivers require that I/O buffer memory is pre-registered (think VFIO,
> > vhost, etc).
> 
> Hi!
> 
> So patches 01-11 are for performance optimization? Don't you have some performance measurements for it?

Hi Vladimir,
I ran the patches against qemu-storage-daemon's vhost-user-blk export
with iodepth=1 bs=512 to see the per-request overhead due to bounce
buffer allocation/mapping:

Name                                   IOPS   Error
bounce-buf                          4373.81 ± 0.01%
registered-buf                     13062.80 ± 0.67%

The BDRV_REQ_REGISTERED_BUF optimization version is about 3x faster.

Note that IOPS is low because the vhost-user-blk vq is not passed
through to the guest yet (Stefano is working on this). The guest is
also using interrupts, not polling (recent Linux virtio_blk.ko drivers
support poll queues).

I'll also include performance results in the next revision of the patch
series.

Stefan

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