linux-kernel - [patch 01/10] x86/aperfmperf: Dont wake idle CPUs in arch_freq_get_on

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Date:   Fri, 15 Apr 2022 21:19:50 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     x86@...nel.org, "Rafael J. Wysocki" <rafael@...nel.org>,
        linux-pm@...r.kernel.org, Eric Dumazet <edumazet@...gle.com>,
        "Paul E. McKenney" <paulmck@...nel.org>
Subject: [patch 01/10] 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@...utronix.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);