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authorGiovanni Gherdovich <ggherdovich@suse.cz>2020-04-16 08:47:42 +0300
committerPeter Zijlstra <peterz@infradead.org>2020-04-23 00:10:13 +0300
commit9a6c2c3c7a73ce315c57c1b002caad6fcc858d0f (patch)
treebf911ce30eb55bcf938b38019f6ba355d8644a26 /arch
parentae83d0b416db002fe95601e7f97f64b59514d936 (diff)
downloadlinux-9a6c2c3c7a73ce315c57c1b002caad6fcc858d0f.tar.xz
x86, sched: Bail out of frequency invariance if base frequency is unknown
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. Fixes: 1567c3e3467c ("x86, sched: Add support for frequency invariance") Signed-off-by: Giovanni Gherdovich <ggherdovich@suse.cz> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> Link: https://lkml.kernel.org/r/20200416054745.740-2-ggherdovich@suse.cz
Diffstat (limited to 'arch')
-rw-r--r--arch/x86/kernel/smpboot.c9
1 files changed, 9 insertions, 0 deletions
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());