Messages in this thread Patch in this message | | | From | "Rafael J. Wysocki" <> | Subject | Re: [PATCH v3] cpuidle: poll_state: Add time limit to poll_idle() | Date | Thu, 22 Mar 2018 18:09:23 +0100 |
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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.
Does it improve if you do something like the below on top of it?
> 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; }
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