Re: [PATCH V2] scsi: put hot fields of scsi_host_template into one cacheline

Ming Lei
2020-04-23T01:49:07Z

On Wed, Apr 22, 2020 at 07:41:30AM -0700, James Bottomley wrote:
> On Wed, 2020-04-22 at 17:54 +0800, Ming Lei wrote:
> > The following three fields of scsi_host_template are referenced in
> > scsi IO submission path, so put them together into one cacheline:
> >
> > - cmd_size
> > - queuecommand
> > - commit_rqs
>
> Are there benchmarks to show this actually makes a difference, if so,
> how much?

Originally I observed 40% IOPS boost on scsi_debug by moving the three
fields into scsi_host, but I lost that test environment now.

When I run fio on scsi_debug in another machine, IOPS gets ~10% boost
with this patch.

Thanks,
Ming