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: 1567c3e3467c ("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

diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index 18d292f..20e1cea 100644 (file)
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -2002,9 +2002,11 @@ out:
        /*
         * Some hypervisors advertise X86_FEATURE_APERFMPERF
         * 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) {
-               pr_debug("Couldn't determine cpu base frequency, necessary for scale-invariant accounting.\n");
+       if (!base_freq || !turbo_freq) {
+               pr_debug("Couldn't determine cpu base or turbo frequency, necessary for scale-invariant accounting.\n");
                return false;
        }