linux-kernel - [tip: sched/core] x86, sched: Bail out of frequency invariance if turbo frequency is unknown

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Message-ID: <159231011472.16989.10542283129872543886.tip-bot2@tip-bot2>
Date:   Tue, 16 Jun 2020 12:21:54 -0000
From:   "tip-bot2 for Giovanni Gherdovich" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>,
        Giovanni Gherdovich <ggherdovich@...e.cz>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        x86 <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>
Subject: [tip: sched/core] x86, sched: Bail out of frequency invariance if
 turbo frequency is unknown

The following commit has been merged into the sched/core branch of tip:

Commit-ID:     51beea8862a3095559862df39554f05042e1195b
Gitweb:        https://git.kernel.org/tip/51beea8862a3095559862df39554f05042e1195b
Author:        Giovanni Gherdovich <ggherdovich@...e.cz>
AuthorDate:    Sun, 31 May 2020 20:24:52 +02:00
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Mon, 15 Jun 2020 14:10:02 +02:00

x86, sched: Bail out of frequency invariance if turbo frequency is unknown

There may be CPUs that support turbo boost but don't declare any turbo
ratio, i.e. their MSR_TURBO_RATIO_LIMIT is all zeroes. In that condition
scale-invariant calculations can't be performed.

Fixes: 1567c3e3467c ("x86, sched: Add support for frequency invariance")
Suggested-by: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
Signed-off-by: Giovanni Gherdovich <ggherdovich@...e.cz>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
Tested-by: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
Link: https://lkml.kernel.org/r/20200531182453.15254-3-ggherdovich@suse.cz
---
 arch/x86/kernel/smpboot.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index 18d292f..20e1cea 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -2002,9 +2002,11 @@ out:
 	/*
 	 * Some hypervisors advertise X86_FEATURE_APERFMPERF
 	 * but then fill all MSR's with zeroes.
+	 * Some CPUs have turbo boost but don't declare any turbo ratio
+	 * in MSR_TURBO_RATIO_LIMIT.
 	 */
-	if (!base_freq) {
-		pr_debug("Couldn't determine cpu base frequency, necessary for scale-invariant accounting.\n");
+	if (!base_freq || !turbo_freq) {
+		pr_debug("Couldn't determine cpu base or turbo frequency, necessary for scale-invariant accounting.\n");
 		return false;
 	}