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Date: Mon, 15 Sep 2014 20:28:50 +0100 From: Morten Rasmussen <morten.rasmussen@....com> To: Peter Zijlstra <peterz@...radead.org> Cc: Vincent Guittot <vincent.guittot@...aro.org>, "mingo@...nel.org" <mingo@...nel.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "preeti@...ux.vnet.ibm.com" <preeti@...ux.vnet.ibm.com>, "linux@....linux.org.uk" <linux@....linux.org.uk>, "linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>, "riel@...hat.com" <riel@...hat.com>, "efault@....de" <efault@....de>, "nicolas.pitre@...aro.org" <nicolas.pitre@...aro.org>, "linaro-kernel@...ts.linaro.org" <linaro-kernel@...ts.linaro.org>, "daniel.lezcano@...aro.org" <daniel.lezcano@...aro.org>, Dietmar Eggemann <Dietmar.Eggemann@....com> Subject: Re: [PATCH v5 10/12] sched: get CPU's utilization statistic On Thu, Sep 11, 2014 at 01:34:12PM +0100, Peter Zijlstra wrote: > > @@ -4514,6 +4519,17 @@ static int select_idle_sibling(struct task_struct *p, int target) > > return target; > > } > > > > +static int get_cpu_utilization(int cpu) > > +{ > > + unsigned long usage = cpu_rq(cpu)->cfs.usage_load_avg; > > + unsigned long capacity = capacity_of(cpu); > > + > > + if (usage >= SCHED_LOAD_SCALE) > > + return capacity + 1; > > + > > + return (usage * capacity) >> SCHED_LOAD_SHIFT; > > +} > > So if I understood patch 9 correct, your changelog is iffy. > usage_load_avg should never get > 1 (of whatever unit), no matter how > many tasks are on the rq. You can only maximally run all the time. > > Therefore I can only interpret the if (usage >= SCHED_LOAD_SCALE) as > numerical error handling, nothing more. That is not entirely true unless you also classify transient usage spikes due to task migrations as numerical errors as well. Since each task sched_entity is carrying around 350ms worth of execution history with it between different cpus and cpu utilization is based on the sum of task entity usage_avg_contrib on the runqueue you may get cfs.usage_load_avg > 1 temporarily after task migrations. It will eventually converge to 1. The same goes for new tasks which are initialized to have a usage_avg_contrib of 1 and may be queued on cpu with tasks already running. In that case cfs.usage_load_avg is temporarily unbounded. > Also I'm not entirely sure I like the usage, utilization names/metrics. > I would suggest to reverse them. Call the pure running number > 'utilization' and this scaled with capacity 'usage' or so. I can agree with calling running for utilization, but I'm not convienced about capacity. What does it exactly cover here? I'm confused and jetlagged. Morten -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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