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,
Mel Gorman <mgorman@techsingularity.net>,
Doug Smythies <dsmythies@telus.net>,
Like Xu <like.xu@linux.intel.com>,
Neil Rickert <nwr10cst-oslnx@yahoo.com>,
Chris Wilson <chris@chris-wilson.co.uk>,
Giovanni Gherdovich <ggherdovich@suse.cz>
Subject: [PATCH 1/4] x86, sched: Bail out of frequency invariance if base frequency is unknown
Date: Thu, 16 Apr 2020 07:47:42 +0200 [thread overview]
Message-ID: <20200416054745.740-2-ggherdovich@suse.cz> (raw)
In-Reply-To: <20200416054745.740-1-ggherdovich@suse.cz>
Some hypervisors such as VMWare ESXi 5.5 advertise support for
X86_FEATURE_APERFMPERF but then fill all MSR's with zeroes. In particular,
MSR_PLATFORM_INFO set to zero tricks the code that wants to know the base
clock frequency of the CPU (highest non-turbo frequency), producing a
division by zero when computing the ratio turbo_freq/base_freq necessary
for frequency invariant accounting.
It is to be noted that even if MSR_PLATFORM_INFO contained the appropriate
data, APERF and MPERF are constantly zero on ESXi 5.5, thus freq-invariance
couldn't be done in principle (not that it would make a lot of sense in a
VM anyway). The real problem is advertising X86_FEATURE_APERFMPERF. This
appears to be fixed in more recent versions: ESXi 6.7 doesn't advertise
that feature.
Signed-off-by: Giovanni Gherdovich <ggherdovich@suse.cz>
Fixes: 1567c3e3467c ("x86, sched: Add support for frequency invariance")
---
arch/x86/kernel/smpboot.c | 9 +++++++++
1 file changed, 9 insertions(+)
diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index fe3ab9632f3b..3a318ec9bc17 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -1985,6 +1985,15 @@ static bool intel_set_max_freq_ratio(void)
return false;
out:
+ /*
+ * Some hypervisors advertise X86_FEATURE_APERFMPERF
+ * but then fill all MSR's with zeroes.
+ */
+ if (!base_freq) {
+ pr_debug("Couldn't determine cpu base frequency, necessary for scale-invariant accounting.\n");
+ return false;
+ }
+
arch_turbo_freq_ratio = div_u64(turbo_freq * SCHED_CAPACITY_SCALE,
base_freq);
arch_set_max_freq_ratio(turbo_disabled());
--
2.16.4
next prev parent reply other threads:[~2020-04-16 5:48 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-16 5:47 [PATCH 0/4] Frequency invariance fixes for x86 Giovanni Gherdovich
2020-04-16 5:47 ` Giovanni Gherdovich [this message]
2020-04-16 6:41 ` [PATCH 1/4] x86, sched: Bail out of frequency invariance if base frequency is unknown Giovanni Gherdovich
2020-04-16 15:41 ` Rafael J. Wysocki
2020-04-22 17:15 ` Ricardo Neri
2020-04-23 8:06 ` Giovanni Gherdovich
2020-04-24 1:32 ` Ricardo Neri
2020-04-24 5:53 ` Giovanni Gherdovich
2020-04-22 21:20 ` [tip: sched/urgent] " tip-bot2 for Giovanni Gherdovich
2020-04-16 5:47 ` [PATCH 2/4] x86, sched: Account for CPUs with less than 4 cores in freq. invariance Giovanni Gherdovich
2020-04-16 15:26 ` Dave Kleikamp
2020-04-22 21:20 ` [tip: sched/urgent] " tip-bot2 for Giovanni Gherdovich
2020-04-16 5:47 ` [PATCH 3/4] x86, sched: Don't enable static key when starting secondary CPUs Giovanni Gherdovich
2020-04-22 21:20 ` [tip: sched/urgent] " tip-bot2 for Peter Zijlstra (Intel)
2020-04-16 5:47 ` [PATCH 4/4] x86, sched: Move check for CPU type to caller function Giovanni Gherdovich
2020-04-22 21:20 ` [tip: sched/urgent] " tip-bot2 for Giovanni Gherdovich
2020-04-16 7:20 ` [PATCH 0/4] Frequency invariance fixes for x86 Peter Zijlstra
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