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

[Ming Lei]

Hello Thomas and Guys,

On Mon, Aug 5, 2019 at 9:19 AM Ming Lei <ming.lei@xxxxxxxxxx> 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@xxxxxxx>
> Cc: Christoph Hellwig <hch@xxxxxx>
> Cc: Bjorn Helgaas <helgaas@xxxxxxxxxx>
> Cc: Jens Axboe <axboe@xxxxxxxxx>
> Cc: linux-block@xxxxxxxxxxxxxxx
> Cc: Sagi Grimberg <sagi@xxxxxxxxxxx>
> Cc: linux-nvme@xxxxxxxxxxxxxxxxxxx
> Cc: linux-pci@xxxxxxxxxxxxxxx
> Cc: Keith Busch <keith.busch@xxxxxxxxx>
> Cc: Sumit Saxena <sumit.saxena@xxxxxxxxxxxx>
> Cc: Kashyap Desai <kashyap.desai@xxxxxxxxxxxx>
> Cc: Shivasharan Srikanteshwara <shivasharan.srikanteshwara@xxxxxxxxxxxx>
> Fixes: c66d4bd110a1f8 ("genirq/affinity: Add new callback for (re)calculating interrupt sets")
> Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx>
> ---
>  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