Re: [PATCH V2 3/6] scsi: add flag of .use_managed_irq to 'struct Scsi_Host'

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

On Tue, Jul 06, 2021 at 12:32:27PM +0200, Hannes Reinecke wrote:
> On 7/6/21 9:41 AM, Ming Lei wrote:
> > On Tue, Jul 06, 2021 at 07:37:19AM +0200, Christoph Hellwig wrote:
> > > On Mon, Jul 05, 2021 at 05:55:49PM +0800, Ming Lei wrote:
> > > > The thing is that blk_mq_pci_map_queues() is allowed to be called for
> > > > non-managed irqs. Also some managed irq consumers don't use blk_mq_pci_map_queues().
> > > > 
> > > > So this way just provides hint about managed irq uses, but we really
> > > > need to get this flag set if driver uses managed irq.
> > > 
> > > blk_mq_pci_map_queues is absolutely intended to only be used by
> > > managed irqs.  I wonder if we can enforce that somehow?
> > 
> > It may break some scsi drivers.
> > 
> > And blk_mq_pci_map_queues() just calls pci_irq_get_affinity() to
> > retrieve the irq's affinity, and the irq can be one non-managed irq,
> > which affinity is set via either irq_set_affinity_hint() from kernel
> > or /proc/irq/.
> > 
> But that's static, right? IE blk_mq_pci_map_queues() will be called once
> during module init; so what happens if the user changes the mapping later
> on? How will that be transferred to the driver?

Yeah, that may not work well enough, but still works since non-managed
irq supports migration.

And there are several SCSI drivers which provide module parameter to
enable/disable managed irq, meantime blk_mq_pci_map_queues() is always
called for mapping queues.


Thanks,
Ming