From: Thomas Gleixner <tglx@linutronix.de>
Date: Fri, 15 Apr 2022 19:19:50 +0000 (+0200)
Subject: x86/aperfmperf: Dont wake idle CPUs in arch_freq_get_on_cpu()
X-Git-Tag: v5.19-rc1~227^2~14
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=6d108c96bf23598cc3b4f91d60e9b7694abcd2a7;p=thirdparty%2Flinux.git

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 9ca008f9e9b1a..ea9160f7aaadd 100644
--- 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);