Re: [PATCH 7/9] scsi: hisi_sas_v3: convert private reply queue to blk-mq hw queue

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

On Mon, Jun 03, 2019 at 02:00:19PM +0100, John Garry wrote:
> On 03/06/2019 12:00, Ming Lei wrote:
> > On Fri, May 31, 2019 at 12:38:10PM +0100, John Garry wrote:
> > > 
> > > > > > -fallback:
> > > > > > -     for_each_possible_cpu(cpu)
> > > > > > -             hisi_hba->reply_map[cpu] = cpu % hisi_hba->queue_count;
> > > > > > -     /* Don't clean all CQ masks */
> > > > > > -}
> > > > > > -
> > > > > >  static int interrupt_init_v3_hw(struct hisi_hba *hisi_hba)
> > > > > >  {
> > > > > >       struct device *dev = hisi_hba->dev;
> > > > > > @@ -2383,11 +2359,6 @@ static int interrupt_init_v3_hw(struct hisi_hba *hisi_hba)
> > > > > > 
> > > > > >               min_msi = MIN_AFFINE_VECTORS_V3_HW;
> > > > > > 
> > > > > > -             hisi_hba->reply_map = devm_kcalloc(dev, nr_cpu_ids,
> > > > > > -                                                sizeof(unsigned int),
> > > > > > -                                                GFP_KERNEL);
> > > > > > -             if (!hisi_hba->reply_map)
> > > > > > -                     return -ENOMEM;
> > > > > >               vectors = pci_alloc_irq_vectors_affinity(hisi_hba->pci_dev,
> > > > > >                                                        min_msi, max_msi,
> > > > > >                                                        PCI_IRQ_MSI |
> > > > > > @@ -2395,7 +2366,6 @@ static int interrupt_init_v3_hw(struct hisi_hba *hisi_hba)
> > > > > >                                                        &desc);
> > > > > >               if (vectors < 0)
> > > > > >                       return -ENOENT;
> > > > > > -             setup_reply_map_v3_hw(hisi_hba, vectors - BASE_VECTORS_V3_HW);
> > > > > >       } else {
> > > > > >               min_msi = max_msi;
> > > > > >               vectors = pci_alloc_irq_vectors(hisi_hba->pci_dev, min_msi,
> > > > > > @@ -2896,6 +2866,18 @@ static void debugfs_snapshot_restore_v3_hw(struct hisi_hba *hisi_hba)
> > > > > >       clear_bit(HISI_SAS_REJECT_CMD_BIT, &hisi_hba->flags);
> > > > > >  }
> > > > > > 
> > > > > > +static int hisi_sas_map_queues(struct Scsi_Host *shost)
> > > > > > +{
> > > > > > +     struct hisi_hba *hisi_hba = shost_priv(shost);
> > > > > > +     struct blk_mq_queue_map *qmap = &shost->tag_set.map[HCTX_TYPE_DEFAULT];
> > > > > > +
> > > > > > +     if (auto_affine_msi_experimental)
> > > > > > +             return blk_mq_pci_map_queues(qmap, hisi_hba->pci_dev,
> > > > > > +                             BASE_VECTORS_V3_HW);
> > > > > > +     else
> > > > > > +             return blk_mq_map_queues(qmap);
> > > 
> > > I don't think that the mapping which blk_mq_map_queues() creates are not
> > > want we want. I'm guessing that we still would like a mapping similar to
> > > what blk_mq_pci_map_queues() produces, which is an even spread, putting
> > > adjacent CPUs on the same queue.
> > > 
> > > For my system with 96 cpus and 16 queues, blk_mq_map_queues() would map
> > > queue 0 to cpu 0, 16, 32, 48 ..., queue 1 to cpu 1, 17, 33 and so on.
> > 
> 
> Hi Ming,
> 
> > blk_mq_map_queues() is the default or fallback mapping in case that managed
> > irq isn't used. If the mapping isn't good enough, we still can improve it
> > in future, then any driver applying it can got improved.
> > 
> 
> That's the right attitude. However, as I see, we can only know the mapping
> when we know the interrupt affinity or some other mapping restriction or
> rule etc, which we don't know in this case.
> 
> For now, personally I would rather if we only expose multiple queues for
> when auto_affine_msi_experimental is set. I fear that we may make a
> performance regression for !auto_affine_msi_experimental with this patch. We
> would need to test.

I suggest to use the blk-mq generic helper.

The default queue mapping of blk_mq_map_queues() has been used for a
while, so far so good, such as, very similar way is applied on
megaraid_sas and mpt3sas, see _base_assign_reply_queues() and
megasas_setup_reply_map().

If performance drop is caused, just report it out, we could fix it.
Or even you can write a new .map_queues method just for hisi_sas v3.


Thanks,
Ming