Commit 51beea88 authored May 31, 2020 by Giovanni Gherdovich Committed by Peter Zijlstra Jun 15, 2020

x86, sched: Bail out of frequency invariance if turbo frequency is unknown

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.

Fixes: 1567c3e3 ("x86, sched: Add support for frequency invariance")
Suggested-by: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
Signed-off-by: Giovanni Gherdovich <ggherdovich@suse.cz>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Tested-by: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
Link: https://lkml.kernel.org/r/20200531182453.15254-3-ggherdovich@suse.cz

parent e2b0d619

arch/x86/kernel/smpboot.c

+4 −2

Original line number	Original line	Diff line number	Diff line
	@@ -2002,9 +2002,11 @@ static bool intel_set_max_freq_ratio(void)
	/*		/*
	* Some hypervisors advertise X86_FEATURE_APERFMPERF		* Some hypervisors advertise X86_FEATURE_APERFMPERF
	* but then fill all MSR's with zeroes.		* 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) {		if (!base_freq \|\| !turbo_freq) {
	pr_debug("Couldn't determine cpu base frequency, necessary for scale-invariant accounting.\n");		pr_debug("Couldn't determine cpu base or turbo frequency, necessary for scale-invariant accounting.\n");
	return false;		return false;
	}		}