[patch 01/10] x86/aperfmperf: Dont wake idle CPUs in arch_freq_get_on_cpu()

Thomas Gleixner
2022-04-15T19:20:16Z

aperfmperf_get_khz() already excludes idle CPUs from APERF/MPERF sampling
and that's a reasonable decision. There is no point in sending up to two
IPIs to an idle CPU just because someone reads a sysfs file.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
arch/x86/kernel/cpu/aperfmperf.c | 3 +++
1 file changed, 3 insertions(+)

--- a/arch/x86/kernel/cpu/aperfmperf.c
+++ b/arch/x86/kernel/cpu/aperfmperf.c
@@ -139,6 +139,9 @@ unsigned int arch_freq_get_on_cpu(int cp
if (!housekeeping_cpu(cpu, HK_TYPE_MISC))
return 0;

+ if (rcu_is_idle_cpu(cpu))
+ return 0;
+
if (aperfmperf_snapshot_cpu(cpu, ktime_get(), true))
return per_cpu(samples.khz, cpu);