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Message-ID: <20170410112607.GD30804@e106622-lin>
Date: Mon, 10 Apr 2017 12:26:07 +0100
From: Juri Lelli <juri.lelli@....com>
To: "Rafael J. Wysocki" <rjw@...ysocki.net>
Cc: Linux PM <linux-pm@...r.kernel.org>,
LKML <linux-kernel@...r.kernel.org>,
Peter Zijlstra <peterz@...radead.org>,
Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
Viresh Kumar <viresh.kumar@...aro.org>,
Vincent Guittot <vincent.guittot@...aro.org>,
Patrick Bellasi <patrick.bellasi@....com>,
Joel Fernandes <joelaf@...gle.com>,
Morten Rasmussen <morten.rasmussen@....com>
Subject: Re: [RFC/RFT][PATCH 2/2] cpufreq: schedutil: Utilization aggregation
Hi Rafael,
thanks for this set. I'll give it a try (together with your previous
patch) in the next few days.
A question below.
On 10/04/17 02:11, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
>
> Due to the limitation of the rate of frequency changes the schedutil
> governor only estimates the CPU utilization entirely when it is about
> to update the frequency for the corresponding cpufreq policy. As a
> result, the intermediate utilization values are discarded by it,
> but that is not appropriate in general (like, for example, when
> tasks migrate from one CPU to another or exit, in which cases the
> utilization measured by PELT may change abruptly between frequency
> updates).
>
> For this reason, modify schedutil to estimate CPU utilization
> completely whenever it is invoked for the given CPU and store the
> maximum encountered value of it as input for subsequent new frequency
> computations. This way the new frequency is always based on the
> maximum utilization value seen by the governor after the previous
> frequency update which effectively prevents intermittent utilization
> variations from causing it to be reduced unnecessarily.
>
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> ---
[...]
> -static void sugov_get_util(unsigned long *util, unsigned long *max)
> +static void sugov_get_util(struct sugov_cpu *sg_cpu, unsigned int flags)
> {
> + unsigned long cfs_util, cfs_max;
> struct rq *rq = this_rq();
> - unsigned long cfs_max;
>
> - cfs_max = arch_scale_cpu_capacity(NULL, smp_processor_id());
> + sg_cpu->flags |= flags & SCHED_CPUFREQ_RT_DL;
> + if (sg_cpu->flags & SCHED_CPUFREQ_RT_DL)
> + return;
>
IIUC, with this you also keep track of any RT/DL tasks that woke up
during the last throttling period, and react accordingly as soon a
triggering event happens after the throttling period elapses.
Given that for RT (and still for DL as well) the next event is a
periodic tick, couldn't happen that the required frequency transition
for an RT task, that unfortunately woke up before the end of a throttling
period, gets delayed of a tick interval (at least 4ms on ARM)?
Don't we need to treat such wake up events (RT/DL) in a special way and
maybe set a timer to fire and process them as soon as the current
throttling period elapses? Might be a patch on top of this I guess.
Best,
- Juri
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