genirq/affinity: Spread IRQs to all available NUMA nodes

longlimsft · KAGA-KOKO · commit b82592199032 · 2018-11-05T12:16:26.000+01:00
If the number of NUMA nodes exceeds the number of MSI/MSI-X interrupts which are allocated for a device, the interrupt affinity spreading code fails to spread them across all nodes. The reason is, that the spreading code starts from node 0 and continues up to the number of interrupts requested for allocation. This leaves the nodes past the last interrupt unused. This results in interrupt concentration on the first nodes which violates the assumption of the block layer that all nodes are covered evenly. As a consequence the NUMA nodes above the number of interrupts are all assigned to hardware queue 0 and therefore NUMA node 0, which results in bad performance and has CPU hotplug implications, because queue 0 gets shut down when the last CPU of node 0 is offlined. Go over all NUMA nodes and assign them round-robin to all requested interrupts to solve this. [ tglx: Massaged changelog ] Signed-off-by: Long Li <longli@microsoft.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Reviewed-by: Ming Lei <ming.lei@redhat.com> Cc: Michael Kelley <mikelley@microsoft.com> Link: https://lkml.kernel.org/r/20181102180248.13583-1-longli@linuxonhyperv.com
diff --git a/kernel/irq/affinity.c b/kernel/irq/affinity.c
@@ -117,12 +117,11 @@ static int irq_build_affinity_masks(const struct irq_affinity *affd,
 	 */
 	if (numvecs <= nodes) {
 		for_each_node_mask(n, nodemsk) {
-			cpumask_copy(masks + curvec, node_to_cpumask[n]);
-			if (++done == numvecs)
-				break;
+			cpumask_or(masks + curvec, masks + curvec, node_to_cpumask[n]);
 			if (++curvec == last_affv)
 				curvec = affd->pre_vectors;
 		}
+		done = numvecs;
 		goto out;
 	}
 

Original file line number	Diff line number	Diff line change
`@@ -117,12 +117,11 @@ static int irq_build_affinity_masks(const struct irq_affinity *affd,`
`117`	`117`	`*/`
`118`	`118`	`if (numvecs <= nodes) {`
`119`	`119`	`for_each_node_mask(n, nodemsk) {`
`120`		`- cpumask_copy(masks + curvec, node_to_cpumask[n]);`
`121`		`- if (++done == numvecs)`
`122`		`- break;`
	`120`	`+ cpumask_or(masks + curvec, masks + curvec, node_to_cpumask[n]);`
`123`	`121`	`if (++curvec == last_affv)`
`124`	`122`	`curvec = affd->pre_vectors;`
`125`	`123`	`}`
	`124`	`+ done = numvecs;`
`126`	`125`	`goto out;`
`127`	`126`	`}`
`128`	`127`