x86/aperfmperf: Dont wake idle CPUs in arch_freq_get_on_cpu()

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>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Paul E. McKenney <paulmck@kernel.org>
Link: https://lore.kernel.org/r/20220415161206.419880163@linutronix.de

diff --git a/arch/x86/kernel/cpu/aperfmperf.c b/arch/x86/kernel/cpu/aperfmperf.c
index 9ca008f..ea9160f 100644 (file)
--- 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 cpu)
        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);