| Message ID | 20170420124447.13716-1-ville.syrjala@linux.intel.com (mailing list archive) |
|---|---|
| State | Not Applicable, archived |
| Headers | show |
On Thu, Apr 20, 2017 at 03:44:47PM +0300, ville.syrjala@linux.intel.com wrote: > From: Ville Syrjälä <ville.syrjala@linux.intel.com> > > This reverts commit e93e59ce5b85e6c2b444f09fd1f707274ec066dc. > > The TSC stops in deeper C states, so using local_clock() in cpuidle > to track the C state residency seems like a bad idea. With local_clock() > powertop is reporting mostly 0% residency for C states here. Presumably > the core is still spending most of its time in some deep C-state since > the totals typically add up to only 5% or so, so perhaps the governor > isn't getting totally confused by these bogus numbers. But let's go > back to using ktime_get() as that at least works correctly across the > board. The local clock is faster, more accurate and more stable. We saw ktime_get() can be expensive, especially on slower CPUs. Why not add flag for the idle state to tell the local clocksource stops and use in this case ktime_get() ? This flag can be set on the idle state at init time in intel_idle.c around: ... if (((mwait_cstate + 1) > 2) && !boot_cpu_has(X86_FEATURE_NONSTOP_TSC)) mark_tsc_unstable("TSC halts in idle" " states deeper than C2"); ... and in processor_idlec.c around: ... tsc_check_state(cx->type); ... So we keep using local_clock() in most of the cases, for most of the boards. > Note that the code has changed somewhat since the regression happened, > so this isn't a 1:1 revert of the offending commit. > > Cc: stable@vger.kernel.org > Cc: Daniel Lezcano <daniel.lezcano@linaro.org> > Cc: Peter Zijlstra (Intel) <peterz@infradead.org> > Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com> > Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com> > --- > drivers/cpuidle/cpuidle.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c > index 548b90be7685..24a52805527f 100644 > --- a/drivers/cpuidle/cpuidle.c > +++ b/drivers/cpuidle/cpuidle.c > @@ -213,13 +213,13 @@ int cpuidle_enter_state(struct cpuidle_device *dev, struct cpuidle_driver *drv, > sched_idle_set_state(target_state); > > trace_cpu_idle_rcuidle(index, dev->cpu); > - time_start = ns_to_ktime(local_clock()); > + time_start = ktime_get(); > > stop_critical_timings(); > entered_state = target_state->enter(dev, drv, index); > start_critical_timings(); > > - time_end = ns_to_ktime(local_clock()); > + time_end = ktime_get(); > trace_cpu_idle_rcuidle(PWR_EVENT_EXIT, dev->cpu); > > /* The cpu is no longer idle or about to enter idle. */ > -- > 2.10.2 >
diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c index 548b90be7685..24a52805527f 100644 --- a/drivers/cpuidle/cpuidle.c +++ b/drivers/cpuidle/cpuidle.c @@ -213,13 +213,13 @@ int cpuidle_enter_state(struct cpuidle_device *dev, struct cpuidle_driver *drv, sched_idle_set_state(target_state); trace_cpu_idle_rcuidle(index, dev->cpu); - time_start = ns_to_ktime(local_clock()); + time_start = ktime_get(); stop_critical_timings(); entered_state = target_state->enter(dev, drv, index); start_critical_timings(); - time_end = ns_to_ktime(local_clock()); + time_end = ktime_get(); trace_cpu_idle_rcuidle(PWR_EVENT_EXIT, dev->cpu); /* The cpu is no longer idle or about to enter idle. */