Re: [PATCH V4 1/3] driver core: mark device as irq affinity managed if any irq is managed

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

On Mon, Jul 19, 2021 at 11:39:53AM +0100, John Garry wrote:
> On 19/07/2021 10:44, Christoph Hellwig wrote:
> > On Mon, Jul 19, 2021 at 08:51:22AM +0100, John Garry wrote:
> > > > Address this issue by adding one field of .irq_affinity_managed into
> > > > 'struct device'.
> > > > 
> > > > Suggested-by: Christoph Hellwig <hch@lst.de>
> > > > Signed-off-by: Ming Lei <ming.lei@redhat.com>
> > > 
> > > Did you consider that for PCI device we effectively have this info already:
> > > 
> > > bool dev_has_managed_msi_irq(struct device *dev)
> > > {
> > > 	struct msi_desc *desc;
> > > 
> > > 	list_for_each_entry(desc, dev_to_msi_list(dev), list)
> 
> I just noticed for_each_msi_entry(), which is the same
> 
> 
> > > 		if (desc->affinity && desc->affinity->is_managed)
> > > 			return true;
> > > 	}
> > > 
> > > 	return false;
> > 
> > Just walking the list seems fine to me given that this is not a
> > performance criticial path.  But what are the locking implications?
> 
> Since it would be used for sequential setup code, I didn't think any locking
> was required. But would need to consider where that function lived and
> whether it's public.

Yeah, the allocated irq vectors should be live when running map queues.

> 
> > 
> > Also does the above imply this won't work for your platform MSI case?
> > .
> > 
> 
> Right. I think that it may be possible to reach into the platform msi
> descriptors to get this info, but I am not sure it's worth it. There is only
> 1x user there and there is no generic .map_queues function, so could set the
> flag directly:
> 
> int blk_mq_pci_map_queues(struct blk_mq_queue_map *qmap, struct pci_dev
> *pdev,
>  		for_each_cpu(cpu, mask)
>  			qmap->mq_map[cpu] = qmap->queue_offset + queue;
>  	}
> +	qmap->use_managed_irq = dev_has_managed_msi_irq(&pdev->dev);
> }
> 
> --- a/drivers/scsi/hisi_sas/hisi_sas_v2_hw.c
> +++ b/drivers/scsi/hisi_sas/hisi_sas_v2_hw.c
> @@ -3563,6 +3563,8 @@ static int map_queues_v2_hw(struct Scsi_Host *shost)
>                        qmap->mq_map[cpu] = qmap->queue_offset + queue;
>        }
> 
> +       qmap->use_managed_irq = 1;
> +
>        return 0;

virtio can be populated via platform device too, but managed irq affinity
isn't used, so seems dev_has_managed_msi_irq() is fine.


Thanks,
Ming