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

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Date:   Thu, 13 Apr 2017 14:46:03 -0700
From:   tip-bot for Keith Busch <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     keith.busch@...el.com, linux-kernel@...r.kernel.org,
        xiaolong.ye@...el.com, tglx@...utronix.de, hpa@...or.com,
        mingo@...nel.org
Subject: [tip:irq/urgent] irq/affinity: Fix extra vecs calculation

Commit-ID:  3412386b531244f24a27c79ee003506a52a00848
Gitweb:     http://git.kernel.org/tip/3412386b531244f24a27c79ee003506a52a00848
Author:     Keith Busch <keith.busch@...el.com>
AuthorDate: Thu, 13 Apr 2017 13:28:12 -0400
Committer:  Thomas Gleixner <tglx@...utronix.de>
CommitDate: Thu, 13 Apr 2017 23:41:00 +0200

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>
Link: http://lkml.kernel.org/r/1492104492-19943-1-git-send-email-keith.busch@intel.com
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>

---
 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++) {