Messages in this thread | | | Date | Wed, 4 May 2016 13:56:35 +0200 | Subject | Re: [lkp] [sched/fair] 41e0d37f7a: divide error: 0000 [#1] SMP | From | "Rafael J. Wysocki" <> |
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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.
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