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SubjectRe: [PATCH] irq: consider cpus on nodes are unbalanced
Date
Rei,

On Fri, Oct 29 2021 at 17:27, Rei Yamamoto wrote:

Cc'ing a few people who worked on this code.

> If cpus on a node are offline at boot time, there are
> difference in the number of nodes between when building affinity
> masks for present cpus and when building affinity masks for possible
> cpus. This patch fixes 2 problems caused by the difference of the
> number of nodes:
>
> - If some unused vectors remain after building masks for present cpus,
> remained vectors are assigned for building masks for possible cpus.
> Therefore "numvecs <= nodes" condition must be
> "vecs_to_assign <= nodes_to_assign". Fix this problem by making this
> condition appropriate.
>
> - The routine of "numvecs <= nodes" condition can overwrite bits of
> masks for present cpus in building masks for possible cpus. Fix this
> problem by making CPU bits, which is not target, not changing.
>
> Signed-off-by: Rei Yamamoto <yamamoto.rei@jp.fujitsu.com>
> ---
> kernel/irq/affinity.c | 10 ++++++++--
> 1 file changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/irq/affinity.c b/kernel/irq/affinity.c
> index f7ff8919dc9b..1cdf89e5e2fb 100644
> --- a/kernel/irq/affinity.c
> +++ b/kernel/irq/affinity.c
> @@ -267,10 +267,16 @@ static int __irq_build_affinity_masks(unsigned int startvec,
> * If the number of nodes in the mask is greater than or equal the
> * number of vectors we just spread the vectors across the nodes.
> */
> - if (numvecs <= nodes) {
> + if (numvecs - (curvec - firstvec) <= nodes) {
> for_each_node_mask(n, nodemsk) {
> + unsigned int ncpus;
> +
> + cpumask_and(nmsk, cpu_mask, node_to_cpumask[n]);
> + ncpus = cpumask_weight(nmsk);
> + if (!ncpus)
> + continue;
> cpumask_or(&masks[curvec].mask, &masks[curvec].mask,
> - node_to_cpumask[n]);
> + nmsk);
> if (++curvec == last_affv)
> curvec = firstvec;
> }

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