linux-kernel - Re: [RFC PATCH 1/1] cpuidle: teo: Add optional util-awareness

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Date:   Sun, 18 Sep 2022 15:17:02 +0800
From:   Chen Yu <yu.chen.surf@...il.com>
To:     Kajetan Puchalski <kajetan.puchalski@....com>
Cc:     rafael@...nel.org, daniel.lezcano@...aro.org, lukasz.luba@....com,
        Dietmar.Eggemann@....com, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Chen Yu <yu.c.chen@...el.com>,
        Zhang Rui <rui.zhang@...el.com>,
        Len Brown <len.brown@...el.com>
Subject: Re: [RFC PATCH 1/1] cpuidle: teo: Add optional util-awareness

On Fri, Sep 16, 2022 at 12:49 AM Kajetan Puchalski
<kajetan.puchalski@....com> wrote:
>
> Modern interactive systems, such as recent Android phones, tend to have
> power efficient shallow idle states. Selecting deeper idle states on a
> device while a latency-sensitive workload is running can adversely impact
> performance due to increased latency. Additionally, if the CPU wakes up
> from a deeper sleep before its target residency as is often the case, it
> results in a waste of energy on top of that.
>
> This patch extends the TEO governor with an optional mechanism adding
> util-awareness, effectively providing a way for the governor to switch
> between only selecting the shallowest idle state when the cpu is being
> utilized over a certain threshold and trying to select the deepest possible
> state using TEO's metrics when the cpu is not being utilized.
Not sure if we can use util_avg as schedutil, but it looks interesting.
The last time I was trying to propose an idea to leverage util_avg to
optimize some
codes in the kernel, it was suggested that it would be better to make
the stategy
gradual rather than 0,1 state. So I was thinking if we could make it
something like:

next_idx = cpuidle_select();
next_idx = next_idx * (cpu_cap - util_avg) / cpu_cap;

The lower the util_avg is, the more we honor the choice of the governor,
vice versa.
> This is now possible since the CPU utilization is exported from the scheduler with the
> sched_cpu_util function and already used e.g. in the thermal governor IPA.
>
> This can provide drastically decreased latency and performance benefits in
> certain types of mobile workloads that are sensitive to latency,
> such as Geekbench 5.
As Doug mentioned in another thread, the impact data to energy consumption would
also be interesting.

thanks,
Chenyu