Re: [PATCH] PCI/MSI: Only disable affinity settings if pre and post vector count is equal to max_vecs and not min_vecs

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On Wed, Mar 01, 2017 at 03:31:58PM -0800, Himanshu Madhani wrote:
> From: Michael Hernandez <michael.hernandez@xxxxxxxxxx>
> 
> min_vecs is the minimum amount of vectors needed to operate in MSI-X mode
> which may just include the vectors that don't need affinity.
> 
> Disabling affinity settings causes the qla2xxx driver scsi_add_host
> to fail when blk_mq is enabled as the blk_mq_pci_map_queues expects
> affinity masks on each vector.
> 
> v2 --> v3
> o fixed code as per review comments.
> 
> v1 --> v2
> 
> o Moved the check from pci_alloc_irq_vectors_affinity() to
>   __pci_enable_{msi|msix}_range()
> 
> Fixes: dfef358 ("PCI/MSI: Don't apply affinity if there aren't enough vectors left")
> Signed-off-by: Michael Hernandez <michael.hernandez@xxxxxxxxxx>
> Signed-off-by: Himanshu Madhani <himanshu.madhani@xxxxxxxxxx>
> Cc: Christoph Hellwig <hch@xxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx
> ---
>  drivers/pci/msi.c |   25 ++++++++++++++++++-------
>  1 files changed, 18 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/pci/msi.c b/drivers/pci/msi.c
> index 7f73bac..46c0cdd 100644
> --- a/drivers/pci/msi.c
> +++ b/drivers/pci/msi.c
> @@ -1091,6 +1091,15 @@ static int __pci_enable_msi_range(struct pci_dev *dev, int minvec, int maxvec,
>  
>  	for (;;) {
>  		if (affd) {
> +			/*
> +			 * If there aren't any vectors left after applying the
> +			 * pre/post vectors don't bother with assigning
> +			 * affinity.
> +			 */
> +			if (affd->pre_vectors + affd->post_vectors == nvec)
> +				affd = NULL;
> +		}

I don't really like this because affd->pre_vectors and
affd->post_vectors are not PCI MSI concepts.  I think they really
belong in irq/affinity.c, e.g., maybe this could be checked in
irq_create_affinity_masks().

If that could be done, we wouldn't have to duplicate the checks here
for both MSI and MSI-X.

I raised a similar question earlier:
http://lkml.kernel.org/r/20170202173659.GD21267@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

> +		if (affd) {
>  			nvec = irq_calc_affinity_vectors(nvec, affd);
>  			if (nvec < minvec)
>  				return -ENOSPC;
> @@ -1138,6 +1147,15 @@ static int __pci_enable_msix_range(struct pci_dev *dev,
>  
>  	for (;;) {
>  		if (affd) {
> +			/*
> +			 * If there aren't any vectors left after applying the
> +			 * pre/post vectors don't bother with assigning
> +			 * affinity.
> +			 */
> +			if (affd->pre_vectors + affd->post_vectors == nvec)
> +				affd = NULL;
> +		}
> +		if (affd) {
>  			nvec = irq_calc_affinity_vectors(nvec, affd);
>  			if (nvec < minvec)
>  				return -ENOSPC;
> @@ -1209,13 +1227,6 @@ int pci_alloc_irq_vectors_affinity(struct pci_dev *dev, unsigned int min_vecs,
>  
>  		if (affd->pre_vectors + affd->post_vectors > min_vecs)
>  			return -EINVAL;
> -
> -		/*
> -		 * If there aren't any vectors left after applying the pre/post
> -		 * vectors don't bother with assigning affinity.
> -		 */
> -		if (affd->pre_vectors + affd->post_vectors == min_vecs)
> -			affd = NULL;
>  	} else {
>  		if (WARN_ON(affd))
>  			affd = NULL;
> -- 
> 1.7.1
> 



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