[PATCH] genirq/affinity: create affinity mask for single vector

[PATCH] genirq/affinity: create affinity mask for single vector

[Ming Lei]

Since commit c66d4bd110a1f8 ("genirq/affinity: Add new callback for
(re)calculating interrupt sets"), irq_create_affinity_masks() returns
NULL in case of single vector. This change has caused regression on some
drivers, such as lpfc.

The problem is that single vector may be triggered in some generic cases:
1) kdump kernel 2) irq vectors resource is close to exhaustion.

If we don't create affinity mask for single vector, almost every caller
has to handle the special case.

So still create affinity mask for single vector, since irq_create_affinity_masks()
is capable of handling that.

Cc: Marc Zyngier <marc.zyngier at arm.com>
Cc: Christoph Hellwig <hch at lst.de>
Cc: Bjorn Helgaas <helgaas at kernel.org>
Cc: Jens Axboe <axboe at kernel.dk>
Cc: linux-block at vger.kernel.org
Cc: Sagi Grimberg <sagi at grimberg.me>
Cc: linux-nvme at lists.infradead.org
Cc: linux-pci at vger.kernel.org
Cc: Keith Busch <keith.busch at intel.com>
Cc: Sumit Saxena <sumit.saxena at broadcom.com>
Cc: Kashyap Desai <kashyap.desai at broadcom.com>
Cc: Shivasharan Srikanteshwara <shivasharan.srikanteshwara at broadcom.com>
Fixes: c66d4bd110a1f8 ("genirq/affinity: Add new callback for (re)calculating interrupt sets")
Signed-off-by: Ming Lei <ming.lei at redhat.com>
---
 kernel/irq/affinity.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/kernel/irq/affinity.c b/kernel/irq/affinity.c
index 4352b08ae48d..6fef48033f96 100644
--- a/kernel/irq/affinity.c
+++ b/kernel/irq/affinity.c
@@ -251,11 +251,9 @@ irq_create_affinity_masks(unsigned int nvecs, struct irq_affinity *affd)
 	 * Determine the number of vectors which need interrupt affinities
 	 * assigned. If the pre/post request exhausts the available vectors
 	 * then nothing to do here except for invoking the calc_sets()
-	 * callback so the device driver can adjust to the situation. If there
-	 * is only a single vector, then managing the queue is pointless as
-	 * well.
+	 * callback so the device driver can adjust to the situation.
 	 */
-	if (nvecs > 1 && nvecs > affd->pre_vectors + affd->post_vectors)
+	if (nvecs > affd->pre_vectors + affd->post_vectors)
 		affvecs = nvecs - affd->pre_vectors - affd->post_vectors;
 	else
 		affvecs = 0;
-- 
2.20.1

[PATCH] genirq/affinity: create affinity mask for single vector

[Ming Lei]

Hello Thomas and Guys,

On Mon, Aug 5, 2019@9:19 AM Ming Lei <ming.lei@redhat.com> wrote:
>
> Since commit c66d4bd110a1f8 ("genirq/affinity: Add new callback for
> (re)calculating interrupt sets"), irq_create_affinity_masks() returns
> NULL in case of single vector. This change has caused regression on some
> drivers, such as lpfc.
>
> The problem is that single vector may be triggered in some generic cases:
> 1) kdump kernel 2) irq vectors resource is close to exhaustion.
>
> If we don't create affinity mask for single vector, almost every caller
> has to handle the special case.
>
> So still create affinity mask for single vector, since irq_create_affinity_masks()
> is capable of handling that.
>
> Cc: Marc Zyngier <marc.zyngier at arm.com>
> Cc: Christoph Hellwig <hch at lst.de>
> Cc: Bjorn Helgaas <helgaas at kernel.org>
> Cc: Jens Axboe <axboe at kernel.dk>
> Cc: linux-block at vger.kernel.org
> Cc: Sagi Grimberg <sagi at grimberg.me>
> Cc: linux-nvme at lists.infradead.org
> Cc: linux-pci at vger.kernel.org
> Cc: Keith Busch <keith.busch at intel.com>
> Cc: Sumit Saxena <sumit.saxena at broadcom.com>
> Cc: Kashyap Desai <kashyap.desai at broadcom.com>
> Cc: Shivasharan Srikanteshwara <shivasharan.srikanteshwara at broadcom.com>
> Fixes: c66d4bd110a1f8 ("genirq/affinity: Add new callback for (re)calculating interrupt sets")
> Signed-off-by: Ming Lei <ming.lei at redhat.com>
> ---
>  kernel/irq/affinity.c | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
>
> diff --git a/kernel/irq/affinity.c b/kernel/irq/affinity.c
> index 4352b08ae48d..6fef48033f96 100644
> --- a/kernel/irq/affinity.c
> +++ b/kernel/irq/affinity.c
> @@ -251,11 +251,9 @@ irq_create_affinity_masks(unsigned int nvecs, struct irq_affinity *affd)
>          * Determine the number of vectors which need interrupt affinities
>          * assigned. If the pre/post request exhausts the available vectors
>          * then nothing to do here except for invoking the calc_sets()
> -        * callback so the device driver can adjust to the situation. If there
> -        * is only a single vector, then managing the queue is pointless as
> -        * well.
> +        * callback so the device driver can adjust to the situation.
>          */
> -       if (nvecs > 1 && nvecs > affd->pre_vectors + affd->post_vectors)
> +       if (nvecs > affd->pre_vectors + affd->post_vectors)
>                 affvecs = nvecs - affd->pre_vectors - affd->post_vectors;
>         else
>                 affvecs = 0;

Without this patch, kdump kernel may not work, so could you take a look
at this patch?

Thanks,
Ming Lei

[PATCH] genirq/affinity: create affinity mask for single vector

[Keith Busch]

On Mon, Aug 05, 2019@09:19:06AM +0800, Ming Lei wrote:
> Since commit c66d4bd110a1f8 ("genirq/affinity: Add new callback for
> (re)calculating interrupt sets"), irq_create_affinity_masks() returns
> NULL in case of single vector. This change has caused regression on some
> drivers, such as lpfc.
> 
> The problem is that single vector may be triggered in some generic cases:
> 1) kdump kernel 2) irq vectors resource is close to exhaustion.
> 
> If we don't create affinity mask for single vector, almost every caller
> has to handle the special case.
> 
> So still create affinity mask for single vector, since irq_create_affinity_masks()
> is capable of handling that.

Hi Ming,

Looks good to me.

Reviewed-by: Keith Busch <keith.busch at intel.com>
 
> ---
>  kernel/irq/affinity.c | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
> 
> diff --git a/kernel/irq/affinity.c b/kernel/irq/affinity.c
> index 4352b08ae48d..6fef48033f96 100644
> --- a/kernel/irq/affinity.c
> +++ b/kernel/irq/affinity.c
> @@ -251,11 +251,9 @@ irq_create_affinity_masks(unsigned int nvecs, struct irq_affinity *affd)
>  	 * Determine the number of vectors which need interrupt affinities
>  	 * assigned. If the pre/post request exhausts the available vectors
>  	 * then nothing to do here except for invoking the calc_sets()
> -	 * callback so the device driver can adjust to the situation. If there
> -	 * is only a single vector, then managing the queue is pointless as
> -	 * well.
> +	 * callback so the device driver can adjust to the situation.
>  	 */
> -	if (nvecs > 1 && nvecs > affd->pre_vectors + affd->post_vectors)
> +	if (nvecs > affd->pre_vectors + affd->post_vectors)
>  		affvecs = nvecs - affd->pre_vectors - affd->post_vectors;
>  	else
>  		affvecs = 0;
> --