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

From: Keith Busch <kbusch@kernel.org>
To: Ming Lei <ming.lei@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>,
	linux-kernel@vger.kernel.org, Marc Zyngier <marc.zyngier@arm.com>,
	Christoph Hellwig <hch@lst.de>,
	Bjorn Helgaas <helgaas@kernel.org>, Jens Axboe <axboe@kernel.dk>,
	linux-block@vger.kernel.org, Sagi Grimberg <sagi@grimberg.me>,
	linux-nvme@lists.infradead.org, linux-pci@vger.kernel.org,
	Keith Busch <keith.busch@intel.com>,
	Sumit Saxena <sumit.saxena@broadcom.com>,
	Kashyap Desai <kashyap.desai@broadcom.com>,
	Shivasharan Srikanteshwara 
	<shivasharan.srikanteshwara@broadcom.com>
Subject: Re: [PATCH] genirq/affinity: create affinity mask for single vector
Date: Thu, 8 Aug 2019 09:17:40 -0600	[thread overview]
Message-ID: <20190808151740.GA27077@localhost.localdomain> (raw)
In-Reply-To: <20190805011906.5020-1-ming.lei@redhat.com>

On Mon, Aug 05, 2019 at 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@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;
> -- 