Re: [PATCH] genirq/affinity: report extra vectors on uneven nodes

[Thomas Gleixner]

On Wed, 7 Aug 2019, Jon Derrick wrote:

Cc+: Ming, Christoph.

Left context for reference.

> The current irq spreading algorithm spreads vectors amongst cpus evenly
> per node. If a node has more cpus than another node, the extra vectors
> being spread may not be reported back to the caller.
> 
> This is most apparent with the NVMe driver and nr_cpus < vectors, where
> the underreporting results in the caller's WARN being triggered:
> 
> irq_build_affinity_masks()
> ...
> 	if (nr_present < numvecs)
> 		WARN_ON(nr_present + nr_others < numvecs);
> 
> Signed-off-by: Jon Derrick <jonathan.derrick@xxxxxxxxx>
> ---
>  kernel/irq/affinity.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/irq/affinity.c b/kernel/irq/affinity.c
> index 4352b08ae48d..9beafb8c7e92 100644
> --- a/kernel/irq/affinity.c
> +++ b/kernel/irq/affinity.c
> @@ -127,7 +127,8 @@ static int __irq_build_affinity_masks(unsigned int startvec,
>  	}
>  
>  	for_each_node_mask(n, nodemsk) {
> -		unsigned int ncpus, v, vecs_to_assign, vecs_per_node;
> +		unsigned int ncpus, v, vecs_to_assign, total_vecs_to_assign,
> +			vecs_per_node;
>  
>  		/* Spread the vectors per node */
>  		vecs_per_node = (numvecs - (curvec - firstvec)) / nodes;
> @@ -141,14 +142,16 @@ static int __irq_build_affinity_masks(unsigned int startvec,
>  
>  		/* Account for rounding errors */
>  		extra_vecs = ncpus - vecs_to_assign * (ncpus / vecs_to_assign);
> +		total_vecs_to_assign = vecs_to_assign + extra_vecs;
>  
> -		for (v = 0; curvec < last_affv && v < vecs_to_assign;
> +		for (v = 0; curvec < last_affv && v < total_vecs_to_assign;
>  		     curvec++, v++) {
>  			cpus_per_vec = ncpus / vecs_to_assign;
>  
>  			/* Account for extra vectors to compensate rounding errors */
>  			if (extra_vecs) {
>  				cpus_per_vec++;
> +				v++;
>  				--extra_vecs;
>  			}
>  			irq_spread_init_one(&masks[curvec].mask, nmsk,
> -- 
> 2.20.1
> 
>