Le 24 janv. 2013 17:55, "Vincent Guittot" <vincent.guit...@linaro.org> a écrit : > > On 24 January 2013 17:44, Frederic Weisbecker <fweis...@gmail.com> wrote: > > 2012/12/3 Vincent Guittot <vincent.guit...@linaro.org>: > >> With the coupled cpuidle driver (but probably also with other drivers), > >> a CPU loops in a temporary safe state while waiting for other CPUs of its > >> cluster to be ready to enter the coupled C-state. If an IRQ or a softirq > >> occurs, the CPU will stay in this internal loop if there is no need > >> to resched. The SCHED softirq clears the NOHZ and increases > >> nr_busy_cpus. If there is no need to resched, we will not call > >> set_cpu_sd_state_idle because of this internal loop in a cpuidle state. > >> We have to call set_cpu_sd_state_idle in tick_nohz_irq_exit which is used > >> to handle such situation. > > > > I'm a bit confused with this. > > > > set_cpu_sd_state_busy() is only called from nohz_kick_needed(). And it > > checks idle_cpu() before doing anything. So if no task is going to be > > scheduled, idle_cpu() prevents from calling set_cpu_sd_state_busy(). > > > > I'm probably missing something. > > Hi Frederic > > I can't find back the trace that i had saved with the issue but IIRC > the sequence is: > The CPU is kicked for ILB > The wake_list of the CPU becomes not empty so cpu id not idle > CPU wakes up, updates is timer framework and call nohz_kick_needed the > execute the ILB sequence > we don't go out of the cpuidle driver function because we don't need > to resched so we don't clear the busy state >
This sequence is not the right one > I'm going to look for the saved trace to check the sequence above I haven't been able to reproduce the bug that this patch was supposed to solved. The patch 2 and 3 seem enough to fix the nr_busy_cpus field. I will continue to try to reproduce it but it seems that it was a side effect of the 2 others fixes of the series Vincent > > Vincent > > > > > Thanks. > > > >> > >> Signed-off-by: Vincent Guittot <vincent.guit...@linaro.org> > >> --- > >> kernel/time/tick-sched.c | 2 ++ > >> 1 file changed, 2 insertions(+) > >> > >> diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c > >> index 955d35b..b8d74ea 100644 > >> --- a/kernel/time/tick-sched.c > >> +++ b/kernel/time/tick-sched.c > >> @@ -570,6 +570,8 @@ void tick_nohz_irq_exit(void) > >> if (!ts->inidle) > >> return; > >> > >> + set_cpu_sd_state_idle(); > >> + > >> /* Cancel the timer because CPU already waken up from the C-states*/ > >> menu_hrtimer_cancel(); > >> __tick_nohz_idle_enter(ts); > >> -- > >> 1.7.9.5 > >> > >> -- > >> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > >> the body of a message to majord...@vger.kernel.org > >> More majordomo info at http://vger.kernel.org/majordomo-info.html > >> Please read the FAQ at http://www.tux.org/lkml/
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