From 53c1788b7d7720565214a466afffdc818d8c6e5f Mon Sep 17 00:00:00 2001
From: Ming Lei <ming.lei@redhat.com>
Date: Fri, 16 Aug 2019 10:28:48 +0800
Subject: [PATCH] genirq/affinity: Improve __irq_build_affinity_masks()

References: bsc#1174897 ltc#187090
Patch-mainline: v5.4-rc1
Git-commit: 53c1788b7d7720565214a466afffdc818d8c6e5f

One invariant of __irq_build_affinity_masks() is that all CPUs in the
specified masks (cpu_mask AND node_to_cpumask for each node) should be
covered during the spread. Even though all requested vectors have been
reached, it's still required to spread vectors among remained CPUs. A
similar policy has been taken in case of 'numvecs <= nodes' already.

So remove the following check inside the loop:

	if (done >= numvecs)
		break;

Meantime assign at least 1 vector for remaining nodes if 'numvecs' vectors
have been handled already.

Also, if the specified cpumask for one numa node is empty, simply do not
spread vectors on this node.

Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20190816022849.14075-2-ming.lei@redhat.com
Acked-by: Michal Suchanek <msuchanek@suse.de>
---
 kernel/irq/affinity.c | 26 ++++++++++++++++++--------
 1 file changed, 18 insertions(+), 8 deletions(-)

diff --git a/kernel/irq/affinity.c b/kernel/irq/affinity.c
index 6fef48033f96..c7cca942bd8a 100644
--- a/kernel/irq/affinity.c
+++ b/kernel/irq/affinity.c
@@ -129,14 +129,26 @@ 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;
 
-		/* Spread the vectors per node */
-		vecs_per_node = (numvecs - (curvec - firstvec)) / nodes;
-
 		/* Get the cpus on this node which are in the mask */
 		cpumask_and(nmsk, cpu_mask, node_to_cpumask[n]);
-
-		/* Calculate the number of cpus per vector */
 		ncpus = cpumask_weight(nmsk);
+		if (!ncpus)
+			continue;
+
+		/*
+		 * Calculate the number of cpus per vector
+		 *
+		 * Spread the vectors evenly per node. If the requested
+		 * vector number has been reached, simply allocate one
+		 * vector for each remaining node so that all nodes can
+		 * be covered
+		 */
+		if (numvecs > done)
+			vecs_per_node = max_t(unsigned,
+					(numvecs - done) / nodes, 1);
+		else
+			vecs_per_node = 1;
+
 		vecs_to_assign = min(vecs_per_node, ncpus);
 
 		/* Account for rounding errors */
@@ -156,13 +168,11 @@ static int __irq_build_affinity_masks(unsigned int startvec,
 		}
 
 		done += v;
-		if (done >= numvecs)
-			break;
 		if (curvec >= last_affv)
 			curvec = firstvec;
 		--nodes;
 	}
-	return done;
+	return done < numvecs ? done : numvecs;
 }
 
 /*
-- 
2.26.2