On Wed, Oct 02, 2013 at 08:03:39PM +0200, Daniel Lezcano wrote: > On 10/02/2013 06:42 PM, Frederic Weisbecker wrote: > >On Wed, Oct 02, 2013 at 06:22:29PM +0200, Daniel Lezcano wrote: > >>On 10/02/2013 05:57 PM, Frederic Weisbecker wrote: > >>>2013/10/2 Daniel Lezcano <daniel.lezc...@linaro.org>: > >>>>The sleep_length is computed in the tick_nohz_stop_sched_tick function > >>>>but it > >>>>is used later in the code with in between the local irq enabled. > >>>> > >>>>cpu_idle_loop > >>>> tick_nohz_idle_enter [ exits with local irq enabled ] > >>>> __tick_nohz_idle_enter > >>>> tick_nohz_stop_sched_tick > >>>> ... > >>>> > >>>> arch_cpu_idle > >>>> menu_select [ uses here 'sleep_length' ] > >>>> ... > >>>> > >>>>Between the computation of the sleep length and its usage, some interrupts > >>>>may occur, making the sleep length shorter than actually it is because of > >>>>the > >>>>interrupt processing > >>> > >>>So, do you mean that the ts->sleep_length would return a value that is too > >>>long > >>>given that the CPU already spent some time to service the irqs since we > >>>computed > >>>the sleep length in tick_nohz_idle_enter()? > >>> > >>>But then tick_nohz_irq_exit() should take care of that as it calls > >>>again tick_nohz_stop_sched_tick(). > >>>So I'm a bit confused. > >>> > >>>>or different if the timer itself expired. > >>> > >>>Same here, if the timer expired, it triggers an interrupt which can do > >>>two things: > >>> > >>>1) reprogram a new timer and this recompute sleep_length > >>>2) set_need_resched() and then exit the idle loop, so arch_cpu_idle() > >>>won't even > >>>be called. Or the timer interrupts hlt, but then menu_select() was > >>>called before. > >>> > >>>So I probably missed something here. > >> > >>No you did not :) > >> > >>Indeed... At the first glance, this issue sounded so obvious I > >>suspected there must be a trick somewhere but I did not think to > >>look at the irq_exit, the code is very complex. Thanks for > >>clarifying this. > >> > >>For my personal information, is there any particular reason to set > >>an intermediate 'sleep_length' in tick_nohz_stop_sched_tick instead > >>of doing what does this patch ? > > > >May be we could do it that way yeah. Is menu_select() called only there? > >I don't know how much difference that would make. > > Yes, it is called just one time in all the code. The benefit would > be just to cleanup a field in the struct tick_sched.
Yeah, why not. Thanks. > > > -- > <http://www.linaro.org/> Linaro.org │ Open source software for ARM SoCs > > Follow Linaro: <http://www.facebook.com/pages/Linaro> Facebook | > <http://twitter.com/#!/linaroorg> Twitter | > <http://www.linaro.org/linaro-blog/> Blog > -- 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/
