Messages in this thread | | | From | Vincent Guittot <> | Date | Mon, 28 May 2018 16:57:34 +0200 | Subject | Re: [PATCH v5 05/10] cpufreq/schedutil: get max utilization |
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Hi Juri,
On 28 May 2018 at 12:12, Juri Lelli <juri.lelli@redhat.com> wrote: > Hi Vincent, > > On 25/05/18 15:12, Vincent Guittot wrote: >> Now that we have both the dl class bandwidth requirement and the dl class >> utilization, we can use the max of the 2 values when agregating the >> utilization of the CPU. >> >> Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org> >> --- >> kernel/sched/sched.h | 6 +++++- >> 1 file changed, 5 insertions(+), 1 deletion(-) >> >> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h >> index 4526ba6..0eb07a8 100644 >> --- a/kernel/sched/sched.h >> +++ b/kernel/sched/sched.h >> @@ -2194,7 +2194,11 @@ static inline void cpufreq_update_util(struct rq *rq, unsigned int flags) {} >> #ifdef CONFIG_CPU_FREQ_GOV_SCHEDUTIL >> static inline unsigned long cpu_util_dl(struct rq *rq) >> { >> - return (rq->dl.running_bw * SCHED_CAPACITY_SCALE) >> BW_SHIFT; >> + unsigned long util = (rq->dl.running_bw * SCHED_CAPACITY_SCALE) >> BW_SHIFT; > > I'd be tempted to say the we actually want to cap to this one above > instead of using the max (as you are proposing below) or the > (theoretical) power reduction benefits of using DEADLINE for certain > tasks might vanish.
The problem that I'm facing is that the sched_entity bandwidth is removed after the 0-lag time and the rq->dl.running_bw goes back to zero but if the DL task has preempted a CFS task, the utilization of the CFS task will be lower than reality and schedutil will set a lower OPP whereas the CPU is always running. The example with a RT task described in the cover letter can be run with a DL task and will give similar results. avg_dl.util_avg tracks the utilization of the rq seen by the scheduler whereas rq->dl.running_bw gives the minimum to match DL requirement.
> >> + >> + util = max_t(unsigned long, util, READ_ONCE(rq->avg_dl.util_avg)); >> + >> + return util; > > Anyway, just a quick thought. I guess we should experiment with this a > bit. Now, I don't unfortunately have a Arm platform at hand for testing. > Claudio, Luca (now Cc-ed), would you be able to fire some tests with > this change? > > Oh, adding Joel and Alessio as well that experimented with DEADLINE > lately. > > Thanks, > > - Juri
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