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Groups > linux.kernel > #1384148
| From | Wanpeng Li <kernellwp@gmail.com> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | Re: [PATCH] sched/cpufreq: don't trigger cpufreq update w/o real rt/deadline tasks running |
| Date | 2016-04-21 14:30 +0200 |
| Message-ID | <rqlU7-EL-31@gated-at.bofh.it> (permalink) |
| References | (3 earlier) <rq8Nc-71F-37@gated-at.bofh.it> <rq8Nc-71F-35@gated-at.bofh.it> <rqbi2-Ai-3@gated-at.bofh.it> <rqkOm-8hw-15@gated-at.bofh.it> <rqlKp-zM-11@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
2016-04-21 20:12 GMT+08:00 Wanpeng Li <kernellwp@gmail.com>:
> 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;
> [...]
> }
Actually I suspect that there is another cpufreq update w/ delta == 0
due to pick_next_task_rt() currently implementation:
if (prev->sched_class == &rt_sched_class)
update_curr(rq); => rq->curr is still A currently
[...]
put_prev_task(rq, prev);
-> update_curr(rq); => rq->curr is still A currently
Regards,
Wanpeng Li
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[PATCH] sched/cpufreq: don't trigger cpufreq update w/o real rt/deadline tasks running Wanpeng Li <kernellwp@gmail.com> - 2016-04-18 08:00 +0200
Re: [PATCH] sched/cpufreq: don't trigger cpufreq update w/o real rt/deadline tasks running "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2016-04-20 02:30 +0200
Re: [PATCH] sched/cpufreq: don't trigger cpufreq update w/o real rt/deadline tasks running Wanpeng Li <kernellwp@gmail.com> - 2016-04-20 02:50 +0200
Re: [PATCH] sched/cpufreq: don't trigger cpufreq update w/o real rt/deadline tasks running Peter Zijlstra <peterz@infradead.org> - 2016-04-20 16:10 +0200
Re: [PATCH] sched/cpufreq: don't trigger cpufreq update w/o real rt/deadline tasks running "Rafael J. Wysocki" <rafael.j.wysocki@intel.com> - 2016-04-21 00:30 +0200
Re: [PATCH] sched/cpufreq: don't trigger cpufreq update w/o real rt/deadline tasks running Wanpeng Li <kernellwp@gmail.com> - 2016-04-21 03:10 +0200
Re: [PATCH] sched/cpufreq: don't trigger cpufreq update w/o real rt/deadline tasks running "Rafael J. Wysocki" <rafael.j.wysocki@intel.com> - 2016-04-21 13:20 +0200
Re: [PATCH] sched/cpufreq: don't trigger cpufreq update w/o real rt/deadline tasks running Wanpeng Li <kernellwp@gmail.com> - 2016-04-21 14:20 +0200
Re: [PATCH] sched/cpufreq: don't trigger cpufreq update w/o real rt/deadline tasks running Wanpeng Li <kernellwp@gmail.com> - 2016-04-21 14:30 +0200
Re: [PATCH] sched/cpufreq: don't trigger cpufreq update w/o real rt/deadline tasks running Peter Zijlstra <peterz@infradead.org> - 2016-04-21 14:40 +0200
Re: [PATCH] sched/cpufreq: don't trigger cpufreq update w/o real rt/deadline tasks running Wanpeng Li <kernellwp@gmail.com> - 2016-04-21 15:40 +0200
Re: [PATCH] sched/cpufreq: don't trigger cpufreq update w/o real rt/deadline tasks running "Rafael J. Wysocki" <rafael@kernel.org> - 2016-04-21 19:10 +0200
Re: [PATCH] sched/cpufreq: don't trigger cpufreq update w/o real rt/deadline tasks running Peter Zijlstra <peterz@infradead.org> - 2016-04-21 19:20 +0200
Re: [PATCH] sched/cpufreq: don't trigger cpufreq update w/o real rt/deadline tasks running Wanpeng Li <kernellwp@gmail.com> - 2016-04-21 00:30 +0200
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