| Message ID | 20200416054745.740-2-ggherdovich@suse.cz |
|---|---|
| State | New |
| Headers | show |
| Series | Frequency invariance fixes for x86 | expand |
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());
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(+)