Hi,
On 2020-06-25 23:34, Nitesh Narayan Lal wrote:
From: Alex Belits <abelits@xxxxxxxxxxx>
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@xxxxxxxxxxx>
Signed-off-by: Nitesh Narayan Lal <nitesh@xxxxxxxxxx>
---
lib/cpumask.c | 16 +++++++++++-----
1 file changed, 11 insertions(+), 5 deletions(-)
diff --git a/lib/cpumask.c b/lib/cpumask.c
index fb22fb266f93..85da6ab4fbb5 100644
--- 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);
AFAICS, this generally resolves to something based on cpu_possible_mask
rather than cpu_online_mask as before, so could now potentially return
an offline CPU. Was that an intentional change?
I was just looking at the current code since I had the rare presence of
mind to check if something suitable already existed before I start
open-coding "any online CPU, but local node preferred" logic for
handling IRQ affinity in a driver - cpumask_local_spread() appears to be
almost what I want (if a bit more heavyweight), if only it would
actually guarantee an online CPU as the kerneldoc claims :(
Robin.
/* 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;
