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    SubjectRe: [PATCH] x86: tsc: Rework time_cpufreq_notifier()
    On 18-04-19, 16:11, Rafael J. Wysocki wrote:
    > From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
    >
    > There are problems with running time_cpufreq_notifier() on SMP
    > systems.
    >
    > First off, the rdtsc() called from there runs on the CPU executing
    > that code and not necessarily on the CPU whose sched_clock() rate is
    > updated which is questionable at best.
    >
    > Second, in the cases when the frequencies of all CPUs in an SMP
    > system are always in sync, it is not sufficient to update just
    > one of them or the set associated with a given cpufreq policy on
    > frequency changes - all CPUs in the system should be updated and
    > that would require more than a simple transition notifier.
    >
    > Note, however, that the underlying issue (the TSC rate depending on
    > the CPU frequency) has not been present in hardware shipping for the
    > last few years and in quite a few relevant cases (acpi-cpufreq in
    > particular) running time_cpufreq_notifier() will cause the TSC to
    > be marked as unstable anyway.
    >
    > For this reason, make time_cpufreq_notifier() simply mark the TSC
    > as unstable and give up when run on SMP and only try to carry out
    > any adjustments otherwise.
    >
    > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
    > ---
    > arch/x86/kernel/tsc.c | 29 ++++++++++++++---------------
    > 1 file changed, 14 insertions(+), 15 deletions(-)

    Reviewed-by: Viresh Kumar <viresh.kumar@linaro.org>

    --
    viresh

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