Re: [PATCH] blk-mq: set default elevator as deadline in case of hctx shared tagset

[Ming Lei <ming.lei@redhat.com>]

On Tue, Apr 06, 2021 at 11:25:08PM +0100, John Garry wrote:
> On 06/04/2021 04:19, Ming Lei wrote:
> 
> Hi Ming,
> 
> > Yanhui found that write performance is degraded a lot after applying
> > hctx shared tagset on one test machine with megaraid_sas. And turns out
> > it is caused by none scheduler which becomes default elevator caused by
> > hctx shared tagset patchset.
> > 
> > Given more scsi HBAs will apply hctx shared tagset, and the similar
> > performance exists for them too.
> > 
> > So keep previous behavior by still using default mq-deadline for queues
> > which apply hctx shared tagset, just like before.
> 
> I think that there a some SCSI HBAs which have nr_hw_queues > 1 and don't
> use shared sbitmap - do you think that they want want this as well (without
> knowing it)?

I don't know but none has been used for them since the beginning, so not
an regression of shared tagset, but this one is really.



Thanks, 
Ming