lib: Restrict cpumask_local_spread to houskeeping CPUs

The current implementation of cpumask_local_spread() does not respect the
isolated CPUs, i.e., even if a CPU has been isolated for Real-Time task,
it will return it to the caller for pinning of its IRQ threads. Having
these unwanted IRQ threads on an isolated CPU adds up to a latency
overhead.

Restrict the CPUs that are returned for spreading IRQs only to the
available housekeeping CPUs.

Signed-off-by: Alex Belits <abelits@marvell.com>
Signed-off-by: Nitesh Narayan Lal <nitesh@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200625223443.2684-2-nitesh@redhat.com

diff --git a/lib/cpumask.c b/lib/cpumask.c
index fb22fb266f9374e96440da9c9c72ff79501c6fdc..85da6ab4fbb5a6aec694104275878cea5dcaf7ba 100644 (file)
--- a/lib/cpumask.c
+++ b/lib/cpumask.c
@@ -6,6 +6,7 @@
 #include <linux/export.h>
 #include <linux/memblock.h>
 #include <linux/numa.h>
+#include <linux/sched/isolation.h>
 
 /**
  * cpumask_next - get the next cpu in a cpumask
@@ -205,22 +206,27 @@ void __init free_bootmem_cpumask_var(cpumask_var_t mask)
  */
 unsigned int cpumask_local_spread(unsigned int i, int node)
 {
-       int cpu;
+       int cpu, hk_flags;
+       const struct cpumask *mask;
 
+       hk_flags = HK_FLAG_DOMAIN | HK_FLAG_MANAGED_IRQ;
+       mask = housekeeping_cpumask(hk_flags);
        /* Wrap: we always want a cpu. */
-       i %= num_online_cpus();
+       i %= cpumask_weight(mask);
 
        if (node == NUMA_NO_NODE) {
-               for_each_cpu(cpu, cpu_online_mask)
+               for_each_cpu(cpu, mask) {
                        if (i-- == 0)
                                return cpu;
+               }
        } else {
                /* NUMA first. */
-               for_each_cpu_and(cpu, cpumask_of_node(node), cpu_online_mask)
+               for_each_cpu_and(cpu, cpumask_of_node(node), mask) {
                        if (i-- == 0)
                                return cpu;
+               }
 
-               for_each_cpu(cpu, cpu_online_mask) {
+               for_each_cpu(cpu, mask) {
                        /* Skip NUMA nodes, done above. */
                        if (cpumask_test_cpu(cpu, cpumask_of_node(node)))
                                continue;