Re: [PATCH RFC v7 00/12] blk-mq/scsi: Provide hostwide shared tags for SCSI HBAs

Ming Lei
2020-06-11T03:07:35Z

On Thu, Jun 11, 2020 at 01:29:07AM +0800, John Garry wrote:
> Hi all,
>
> Here is v7 of the patchset.
>
> In this version of the series, we keep the shared sbitmap for driver tags,
> and introduce changes to fix up the tag budgeting across request queues (
> and associated debugfs changes).
>
> Some performance figures:
>
> Using 12x SAS SSDs on hisi_sas v3 hw. mq-deadline results are included,
> but it is not always an appropriate scheduler to use.
>
> Tag depth 4000 (default) 260**
>
> Baseline:
> none sched: 2290K IOPS 894K
> mq-deadline sched: 2341K IOPS 2313K
>
> Final, host_tagset=0 in LLDD*
> none sched: 2289K IOPS 703K
> mq-deadline sched: 2337K IOPS 2291K
>
> Final:
> none sched: 2281K IOPS 1101K
> mq-deadline sched: 2322K IOPS 1278K
>
> * this is relevant as this is the performance in supporting but not
> enabling the feature
> ** depth=260 is relevant as some point where we are regularly waiting for
> tags to be available. Figures were are a bit unstable here for testing.
>
> A copy of the patches can be found here:
> https://github.com/hisilicon/kernel-dev/commits/private-topic-blk-mq-shared-tags-rfc-v7
>
> And to progress this series, we the the following to go in first, when ready:
> https://lore.kernel.org/linux-scsi/20200430131904.5847-1-hare@suse.de/

I'd suggest to add options to enable shared tags for null_blk & scsi_debug in V8, so
that it is easier to verify the changes without real hardware.

Thanks,
Ming