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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
This commit is contained in:
Alex Belits 2020-06-25 18:34:41 -04:00 committed by Peter Zijlstra
parent 46609ce227
commit 1abdfe706a
1 changed files with 11 additions and 5 deletions
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16
lib/cpumask.c
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@ -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;