Messages in this thread | | | Subject | Re: [PATCH 1/4] x86, sched: Bail out of frequency invariance if base frequency is unknown | From | Giovanni Gherdovich <> | Date | Thu, 16 Apr 2020 08:41:09 +0200 |
| |
+Dario Faggioli
On Thu, 2020-04-16 at 07:47 +0200, Giovanni Gherdovich wrote: > 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());
| |