linux-kernel - [tip: x86/cleanups] x86/aperfmperf: Dont wake idle CPUs in arch_freq_get_on

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Date:   Wed, 27 Apr 2022 13:56:14 -0000
From:   "tip-bot2 for Thomas Gleixner" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        "Paul E. McKenney" <paulmck@...nel.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: x86/cleanups] x86/aperfmperf: Dont wake idle CPUs in
 arch_freq_get_on_cpu()

The following commit has been merged into the x86/cleanups branch of tip:

Commit-ID:     6d108c96bf23598cc3b4f91d60e9b7694abcd2a7
Gitweb:        https://git.kernel.org/tip/6d108c96bf23598cc3b4f91d60e9b7694abcd2a7
Author:        Thomas Gleixner <tglx@...utronix.de>
AuthorDate:    Fri, 15 Apr 2022 21:19:50 +02:00
Committer:     Thomas Gleixner <tglx@...utronix.de>
CommitterDate: Wed, 27 Apr 2022 15:51:08 +02:00

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

---
 arch/x86/kernel/cpu/aperfmperf.c | 3 +++
 1 file changed, 3 insertions(+)

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