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

Ming Lei
2021-07-17T09:31:10Z

On Fri, Jul 16, 2021 at 03:01:54PM -0500, Bjorn Helgaas wrote:
> On Thu, Jul 15, 2021 at 08:08:42PM +0800, Ming Lei wrote:
> > irq vector allocation with managed affinity may be used by driver, and
> > blk-mq needs this info because managed irq will be shutdown when all
> > CPUs in the affinity mask are offline.
> >
> > The info of using managed irq is often produced by drivers(pci subsystem,
>
> Add space between "drivers" and "(".
> s/pci/PCI/

OK.

>
> Does this "managed IRQ" (or "managed affinity", not sure what the
> correct terminology is here) have something to do with devm?
>
> > platform device, ...), and it is consumed by blk-mq, so different subsystems
> > are involved in this info flow
>
> Add period at end of sentence.

OK.

>
> > 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>
> > ---
> > drivers/base/platform.c | 7 +++++++
> > drivers/pci/msi.c | 3 +++
> > include/linux/device.h | 1 +
> > 3 files changed, 11 insertions(+)
> >
> > diff --git a/drivers/base/platform.c b/drivers/base/platform.c
> > index 8640578f45e9..d28cb91d5cf9 100644
> > --- a/drivers/base/platform.c
> > +++ b/drivers/base/platform.c
> > @@ -388,6 +388,13 @@ int devm_platform_get_irqs_affinity(struct platform_device *dev,
> > ptr->irq[i], ret);
> > goto err_free_desc;
> > }
> > +
> > + /*
> > + * mark the device as irq affinity managed if any irq affinity
> > + * descriptor is managed
> > + */
> > + if (desc[i].is_managed)
> > + dev->dev.irq_affinity_managed = true;
> > }
> >
> > devres_add(&dev->dev, ptr);
> > diff --git a/drivers/pci/msi.c b/drivers/pci/msi.c
> > index 3d6db20d1b2b..7ddec90b711d 100644
> > --- a/drivers/pci/msi.c
> > +++ b/drivers/pci/msi.c
> > @@ -1197,6 +1197,7 @@ int pci_alloc_irq_vectors_affinity(struct pci_dev *dev, unsigned int min_vecs,
> > if (flags & PCI_IRQ_AFFINITY) {
> > if (!affd)
> > affd = &msi_default_affd;
> > + dev->dev.irq_affinity_managed = true;
>
> This is really opaque to me. I can't tell what the connection between
> PCI_IRQ_AFFINITY and irq_affinity_managed is.

Comment for PCI_IRQ_AFFINITY is 'Auto-assign affinity',
'irq_affinity_managed' basically means that irq's affinity is managed by
kernel.

What blk-mq needs is exactly if PCI_IRQ_AFFINITY is applied when
allocating irq vectors. When PCI_IRQ_AFFINITY is used, genirq will
shutdown the irq when all CPUs in the assigned affinity are offline,
then blk-mq has to drain all in-flight IOs which will be completed
via this irq and prevent new IO. That is the connection.

Or you think 'irq_affinity_managed' isn't named well?

>
> AFAICT the only place irq_affinity_managed is ultimately used is
> blk_mq_hctx_notify_offline(), and there's no obvious connection
> between that and this code.

I believe the connection is described in comment.

Thanks,
Ming