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    Subject[PATCH AUTOSEL 5.7 04/58] x86, sched: Bail out of frequency invariance if turbo frequency is unknown
    Date
    From: Giovanni Gherdovich <ggherdovich@suse.cz>

    [ Upstream commit 51beea8862a3095559862df39554f05042e1195b ]

    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
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    arch/x86/kernel/smpboot.c | 6 ++++--
    1 file changed, 4 insertions(+), 2 deletions(-)

    diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
    index 2f24c334a938b..3917a2de1580c 100644
    --- a/arch/x86/kernel/smpboot.c
    +++ b/arch/x86/kernel/smpboot.c
    @@ -1999,9 +1999,11 @@ static bool intel_set_max_freq_ratio(void)
    /*
    * 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;
    }

    --
    2.25.1
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