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From:   Giovanni Gherdovich <ggherdovich@suse.cz>
To:     Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Borislav Petkov <bp@suse.de>, Len Brown <lenb@kernel.org>,
        "Rafael J . Wysocki" <rjw@rjwysocki.net>
Cc:     x86@kernel.org, linux-pm@vger.kernel.org,
        linux-kernel@vger.kernel.org,
        Ricardo Neri <ricardo.neri-calderon@linux.intel.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Giovanni Gherdovich <ggherdovich@suse.cz>
Subject: [PATCH 2/2] x86, sched: Bail out of frequency invariance if turbo frequency is unknown
Date:   Tue, 28 Apr 2020 15:24:50 +0200
Message-Id: <20200428132450.24901-3-ggherdovich@suse.cz>
In-Reply-To: <20200428132450.24901-1-ggherdovich@suse.cz>
References: <20200428132450.24901-1-ggherdovich@suse.cz>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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.

Signed-off-by: Giovanni Gherdovich <ggherdovich@suse.cz>
Suggested-by: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
Fixes: 1567c3e3467c ("x86, sched: Add support for frequency invariance")
---
 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 4718f29a3065..ab2a0df7d1fb 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -1991,9 +1991,11 @@ static bool intel_set_max_freq_ratio(void)
 	/*
 	 * 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;
 	}
 
-- 
2.16.4