Messages in this thread | | | Date | Wed, 4 May 2016 20:04:45 +0800 | Subject | Re: [lkp] [sched/fair] 41e0d37f7a: divide error: 0000 [#1] SMP | From | Wanpeng Li <> |
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2016-05-04 19:56 GMT+08:00 Rafael J. Wysocki <rafael@kernel.org>: > On Wed, May 4, 2016 at 1:51 PM, Wanpeng Li <kernellwp@gmail.com> wrote: >> 2016-05-04 19:44 GMT+08:00 Rafael J. Wysocki <rafael@kernel.org>: >>> On Wed, May 4, 2016 at 2:58 AM, Wanpeng Li <kernellwp@gmail.com> wrote: >>>> 2016-05-03 20:15 GMT+08:00 Rafael J. Wysocki <rafael@kernel.org>: >>>>> On Tue, May 3, 2016 at 10:32 AM, Peter Zijlstra <peterz@infradead.org> wrote: >>>>>> On Tue, May 03, 2016 at 09:10:51AM +0800, kernel test robot wrote: >>>>>>> FYI, we noticed the following commit: >>>>>>> >>>>>>> https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git sched/core >>>>>>> commit 41e0d37f7ac81297c07ba311e4ad39465b8c8295 ("sched/fair: Do not call cpufreq hook unless util changed") >>>>>> >>> >>> [cut] >>> >>>>>> >>>>>> That's intel_pstate.c:get_avg_frequency(), which assumes mperf != 0. It >>>>>> being 0 seems to suggest intel_pstate_sample() hasn't been called yet or >>>>>> so. >>>>> >>>>> Well, what's the tree based on? >>>>> >>>>> The mainline does this: >>>>> >>>>> bool sample_taken = intel_pstate_sample(cpu, time); >>>>> >>>>> if (sample_taken && !hwp_active) >>>>> intel_pstate_adjust_busy_pstate(cpu); >>>>> >>>>> and (the mainline version of) intel_pstate_sample() returns false when >>>>> it is called for the first time after setting the update_util hook. >>>> >>>> The callsites in scheduler will set time to rq_clock(rq) when trigger >>>> sample, so when time 0 will be used even if it is set just before >>>> setting the update_util hook? >>> >>> I'm not sure what you mean. >>> >>> time=0 is special as it will cause intel_pstate_sample() to return >>> false on the next invocation. >> >> Sample is driven by cpufreq_update_util() which uses rq_clock(rq) as >> time parameter, so there is no opportunity to pass time 0 to >> intel_pstate_sample(). > > Right. > > So I should have said that had time=0 been passed to > intel_pstate_sample(), it would have caused it to return false on the > next invocation. :-) > > The way it works is that sample.time is 0 initially, so > intel_pstate_sample() returns false first time it is called and the > second invocation gets all of the deltas as needed.
I see, thanks Rafael. :-)
Regards, Wanpeng Li
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