Messages in this thread | | | Date | Thu, 21 Apr 2016 20:12:59 +0800 | Subject | Re: [PATCH] sched/cpufreq: don't trigger cpufreq update w/o real rt/deadline tasks running | From | Wanpeng Li <> |
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2016-04-21 19:11 GMT+08:00 Rafael J. Wysocki <rafael.j.wysocki@intel.com>: > On 4/21/2016 3:09 AM, Wanpeng Li wrote: >> >> 2016-04-21 6:28 GMT+08:00 Rafael J. Wysocki <rafael.j.wysocki@intel.com>: >>> >>> On 4/21/2016 12:24 AM, Wanpeng Li wrote: >>>> >>>> 2016-04-20 22:01 GMT+08:00 Peter Zijlstra <peterz@infradead.org>: >>>>> >>>>> On Wed, Apr 20, 2016 at 02:32:35AM +0200, Rafael J. Wysocki wrote: >>>>>> >>>>>> On Monday, April 18, 2016 01:51:24 PM Wanpeng Li wrote: >>>>>>> >>>>>>> Sometimes update_curr() is called w/o tasks actually running, it is >>>>>>> captured by: >>>>>>> u64 delta_exec = rq_clock_task(rq) - curr->se.exec_start; >>>>>>> We should not trigger cpufreq update in this case for rt/deadline >>>>>>> classes, and this patch fix it. >>>>>>> >>>>>>> Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com> >>>>>> >>>>>> The signed-off-by tag should agree with the From: header. One way to >>>>>> achieve >>>>>> that is to add an extra From: line at the start of the changelog. >>>>>> >>>>>> That said, this looks like a good catch that should go into 4.6 to me. >>>>>> >>>>>> Peter, what do you think? >>>>> >>>>> I'm confused by the Changelog. *what* ? >>>> >>>> Sometimes .update_curr hook is called w/o tasks actually running, it is >>>> captured by: >>>> >>>> u64 delta_exec = rq_clock_task(rq) - curr->se.exec_start; >>>> >>>> We should not trigger cpufreq update in this case for rt/deadline >>>> classes, and this patch fix it. >>> >>> >>> That's what you wrote in the changelog, no need to repeat that. >>> >>> I guess Peter is asking for more details, though. I actually would like >>> to >>> get some more details here too. Like an example of when the situation in >>> question actually happens. >> >> I add a print to print when delta_exec is zero for rt class, something >> like below: >> >> watchdog/5-48 [005] d... 568.449095: update_curr_rt: rt >> delta_exec is zero >> watchdog/5-48 [005] d... 568.449104: <stack trace> >> => pick_next_task_rt >> => __schedule >> => schedule >> => smpboot_thread_fn >> => kthread >> => ret_from_fork >> watchdog/5-48 [005] d... 568.449105: update_curr_rt: rt >> delta_exec is zero >> watchdog/5-48 [005] d... 568.449111: <stack trace> >> => put_prev_task_rt >> => pick_next_task_idle >> => __schedule >> => schedule >> => smpboot_thread_fn >> => kthread >> => ret_from_fork >> watchdog/6-56 [006] d... 568.510094: update_curr_rt: rt >> delta_exec is zero >> watchdog/6-56 [006] d... 568.510103: <stack trace> >> => pick_next_task_rt >> => __schedule >> => schedule >> => smpboot_thread_fn >> => kthread >> => ret_from_fork >> watchdog/6-56 [006] d... 568.510105: update_curr_rt: rt >> delta_exec is zero >> watchdog/6-56 [006] d... 568.510111: <stack trace> >> => put_prev_task_rt >> => pick_next_task_idle >> => __schedule >> => schedule >> => smpboot_thread_fn >> => kthread >> => ret_from_fork >> [...] > > > And the statement in your changelog follows from this I suppose. How does it > follow, exactly?
For example, rt task A will go to sleep, an rt task B is the next candidate to run.
__schedule() -> deactivate_task(A, DEQUEUE_SLEEP) -> dequeue_task_rt() -> update_curr_rt() -> cpufreq_trigger_update() -> delta_exec = rq_clock_task(rq) - curr->se.exec_start; [...] -> pick_next_task_rt() -> update_curr_rt() => rq->curr is still A currently -> cpufreq_trigger_update() -> delta_exec = rq_clock_task(rq) - curr->se.exec_start; => delta == 0, actually A is not running between these two updates if (likely(prev != next)) { rq->curr = B; [...] }
Regards, Wanpeng Li
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