On 18-04-19, 16:11, Rafael J. Wysocki wrote: > From: Rafael J. Wysocki <rafael.j.wyso...@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.wyso...@intel.com> > --- > arch/x86/kernel/tsc.c | 29 ++++++++++++++--------------- > 1 file changed, 14 insertions(+), 15 deletions(-)
Reviewed-by: Viresh Kumar <viresh.ku...@linaro.org> -- viresh
