Messages in this thread | | | Subject | Re: [PATCH v3] cpuidle: poll_state: Add time limit to poll_idle() | From | Rik van Riel <> | Date | Thu, 22 Mar 2018 13:19:16 -0400 |
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On Thu, 2018-03-22 at 18:09 +0100, Rafael J. Wysocki wrote: > On Thursday, March 22, 2018 5:32:23 PM CET Rik van Riel wrote: > > On Wed, 2018-03-14 at 15:08 +0100, Rafael J. Wysocki wrote: > > > From: Rafael J. Wysocki <rafael.j.wysocki@intel.com> > > > > > > If poll_idle() is allowed to spin until need_resched() returns > > > 'true', > > > it may actually spin for a much longer time than expected by the > > > idle > > > governor, since set_tsk_need_resched() is not always called by > > > the > > > timer interrupt handler. If that happens, the CPU may spend much > > > more time than anticipated in the "polling" state. > > > > > > To prevent that from happening, limit the time of the spinning > > > loop > > > in poll_idle(). > > > > > > Suggested-by: Peter Zijlstra <peterz@infradead.org> > > > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> > > > > So ... about bisecting that other patch series... > > > > It turned out I had this patch, which looks so > > obviously correct, as patch #1 in my series. > > > > It also turned out that this patch is responsible > > for the entire 5-10% increase in CPU use for the > > memcache style workload. > > > > I wonder if keeping an idle HT thread much busier > > than before slows down its sibling, or something > > like that. > > Uhm, sorry about this.
No worries, this is why we do patch reviews and tests in the first place.
> Does it improve if you do something like the below on top of it?
That was my next thing to try, after testing just the idle nohz series by itself :)
I'll push both into the test systems, and will get back to you when I have answers.
> > Let me go test the nohz idle series by itself, > > without this patch. > > OK > > --- > drivers/cpuidle/poll_state.c | 6 ++++++ > 1 file changed, 6 insertions(+) > > Index: linux-pm/drivers/cpuidle/poll_state.c > =================================================================== > --- linux-pm.orig/drivers/cpuidle/poll_state.c > +++ linux-pm/drivers/cpuidle/poll_state.c > @@ -10,6 +10,7 @@ > #include <linux/sched/idle.h> > > #define POLL_IDLE_TIME_LIMIT (TICK_NSEC / 16) > +#define POLL_IDLE_COUNT 1000 > > static int __cpuidle poll_idle(struct cpuidle_device *dev, > struct cpuidle_driver *drv, int > index) > @@ -18,9 +19,14 @@ static int __cpuidle poll_idle(struct cp > > local_irq_enable(); > if (!current_set_polling_and_test()) { > + unsigned int loop_count = 0; > + > while (!need_resched()) { > cpu_relax(); > + if (loop_count++ < POLL_IDLE_COUNT) > + continue; > > + loop_count = 0; > if (local_clock() - time_start > > POLL_IDLE_TIME_LIMIT) > break; > } > > -- All Rights Reversed.[unhandled content-type:application/pgp-signature] | |