linux-kernel - [PATCH] irq/affinity: Fix extra vecs calculation

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Date:   Thu, 13 Apr 2017 13:28:12 -0400
From:   Keith Busch <keith.busch@...el.com>
To:     linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>
Cc:     Xiaolong Ye <xiaolong.ye@...el.com>,
        Keith Busch <keith.busch@...el.com>
Subject: [PATCH] irq/affinity: Fix extra vecs calculation

This fixes a math error calculating the extra_vecs. The error assumed
only 1 cpu per vector, but the value needs to account for the actual
number of cpus per vector in order to get the correct remainder for
extra CPU assignment.

Fixes: 7bf8222b9bd0 ("irq/affinity: Fix CPU spread for unbalanced nodes")
Reported-by: Xiaolong Ye <xiaolong.ye@...el.com>
Signed-off-by: Keith Busch <keith.busch@...el.com>
---
 kernel/irq/affinity.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/irq/affinity.c b/kernel/irq/affinity.c
index dc52911..d052947 100644
--- a/kernel/irq/affinity.c
+++ b/kernel/irq/affinity.c
@@ -108,7 +108,7 @@ irq_create_affinity_masks(int nvecs, const struct irq_affinity *affd)
 		vecs_to_assign = min(vecs_per_node, ncpus);
 
 		/* Account for rounding errors */
-		extra_vecs = ncpus - vecs_to_assign;
+		extra_vecs = ncpus - vecs_to_assign * (ncpus / vecs_to_assign);
 
 		for (v = 0; curvec < last_affv && v < vecs_to_assign;
 		     curvec++, v++) {
-- 
2.7.2