Re: [PATCH] blk-mq: don't fail driver tag allocation because of inactive hctx

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

On Fri, Jun 05, 2020 at 08:24:50AM +0100, John Garry wrote:
> On 05/06/2020 01:59, Ming Lei wrote:
> > > 	hctx5: default 36 37 38 39
> > > 	hctx6: default 40 41 42 43
> > > 	hctx7: default 44 45 46 47
> > > 	hctx8: default 48 49 50 51
> > > 	hctx9: default 52 53 54 55
> > > 	hctx10: default 56 57 58 59
> > > 	hctx11: default 60 61 62 63
> > > 	hctx12: default 0 1 2 3
> > > 	hctx13: default 4 5 6 7
> > > 	hctx14: default 8 9 10 11
> > > 	hctx15: default 12 13 14 15
> > OK, the queue mapping is correct.
> > 
> > As I mentioned in another thread, the real hw tag may be set as wrong.
> > 
> 
> I doubt this.
> 
> And I think that you should also be able to add the same debug to
> blk_mq_hctx_notify_offline() to see that there may be still driver tags
> allocated to when all the scheduler tags are free'd for any test in your
> env.

No, that isn't possible, scheduler tag lifetime covers the whole request's
lifetime.

> 
> > You have to double check your cooked tag allocation algorithm and see if it
> > can work well when more requests than real hw queue depth are queued to hisi_sas,
> > and the correct way is to return SCSI_MLQUEUE_HOST_BUSY from .queuecommand().
> 
> Yeah, the LLDD would just reject requests in that scenario and we would know
> about it from logs etc.
> 
> Anyway, I'll continue to check.

The merged patch is much simpler than before, new request is prevented from being
allocated on the inactive hctx, then drain all in-flight requests on this hctx.

You need to check if the request is queued to hw correctly.

Thanks,
Ming