Re: [Qemu-devel] [question] the patch which affect performance of virtio-scsi

[Paolo Bonzini]

On 03/02/2015 03:31, Wangting (Kathy) wrote:
> Hi Paolo,
> 
> Recently I test IO performance with virtio-scsi, and find out that the patch 
> of
> "virtio-scsi: add support for the any_layout feature" affects IO performance 
> of model
> with 4KB 32iodepth sequence read.
> 
> Why cdb and sense is removed from the struct of VirtIOSCSICmdReq and 
> VirtIOSCSICmdResp?

Because I could not find any other way to implement ANY_LAYOUT, and
virtio 1.0 requires that feature.

The performance however was already improved in commit faf1e1f
(virtio-scsi: Optimize virtio_scsi_init_req, 2014-09-16).

Paolo

> How do you consider the impact of the changes to the performance?
> Although the latest version of qemu can optimize the performance by the way 
> of reading merger,
> I think the affect of this patch cannot be ignored.