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Date: Thu, 24 Nov 2016 02:21:30 +0100
From: "Rafael J. Wysocki" <rjw@...ysocki.net>
To: Stratos Karafotis <stratosk@...aphore.gr>
Cc: Viresh Kumar <viresh.kumar@...aro.org>,
"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4] cpufreq: conservative: Decrease frequency faster when the update deferred
On Wednesday, November 16, 2016 07:26:29 PM Stratos Karafotis wrote:
> Conservative governor changes the CPU frequency in steps.
> That means that if a CPU runs at max frequency, it will need several
> sampling periods to return to min frequency when the workload
> is finished.
>
> If the update function that calculates the load and target frequency
> is deferred, the governor might need even more time to decrease the
> frequency.
>
> This may have impact to power consumption and after all conservative
> should decrease the frequency if there is no workload at every sampling
> rate.
>
> To resolve the above issue calculate the number of sampling periods
> that the update is deferred. Considering that for each sampling period
> conservative should drop the frequency by a freq_step because the
> CPU was idle apply the proper subtraction to requested frequency.
>
> Below, the kernel trace with and without this patch. First an
> intensive workload is applied on a specific CPU. Then the workload
> is removed and the CPU goes to idle.
>
> WITHOUT
>
> <idle>-0 [007] dN.. 620.329153: cpu_idle: state=4294967295 cpu_id=7
> kworker/7:2-556 [007] .... 620.350857: cpu_frequency: state=1700000 cpu_id=7
> kworker/7:2-556 [007] .... 620.370856: cpu_frequency: state=1900000 cpu_id=7
> kworker/7:2-556 [007] .... 620.390854: cpu_frequency: state=2100000 cpu_id=7
> kworker/7:2-556 [007] .... 620.411853: cpu_frequency: state=2200000 cpu_id=7
> kworker/7:2-556 [007] .... 620.432854: cpu_frequency: state=2400000 cpu_id=7
> kworker/7:2-556 [007] .... 620.453854: cpu_frequency: state=2600000 cpu_id=7
> kworker/7:2-556 [007] .... 620.494856: cpu_frequency: state=2900000 cpu_id=7
> kworker/7:2-556 [007] .... 620.515856: cpu_frequency: state=3100000 cpu_id=7
> kworker/7:2-556 [007] .... 620.536858: cpu_frequency: state=3300000 cpu_id=7
> kworker/7:2-556 [007] .... 620.557857: cpu_frequency: state=3401000 cpu_id=7
> <idle>-0 [007] d... 669.591363: cpu_idle: state=4 cpu_id=7
> <idle>-0 [007] d... 669.591939: cpu_idle: state=4294967295 cpu_id=7
> <idle>-0 [007] d... 669.591980: cpu_idle: state=4 cpu_id=7
> <idle>-0 [007] dN.. 669.591989: cpu_idle: state=4294967295 cpu_id=7
> ...
> <idle>-0 [007] d... 670.201224: cpu_idle: state=4 cpu_id=7
> <idle>-0 [007] d... 670.221975: cpu_idle: state=4294967295 cpu_id=7
> kworker/7:2-556 [007] .... 670.222016: cpu_frequency: state=3300000 cpu_id=7
> <idle>-0 [007] d... 670.222026: cpu_idle: state=4 cpu_id=7
> <idle>-0 [007] d... 670.234964: cpu_idle: state=4294967295 cpu_id=7
> ...
> <idle>-0 [007] d... 670.801251: cpu_idle: state=4 cpu_id=7
> <idle>-0 [007] d... 671.236046: cpu_idle: state=4294967295 cpu_id=7
> kworker/7:2-556 [007] .... 671.236073: cpu_frequency: state=3100000 cpu_id=7
> <idle>-0 [007] d... 671.236112: cpu_idle: state=4 cpu_id=7
> <idle>-0 [007] d... 671.393437: cpu_idle: state=4294967295 cpu_id=7
> ...
> <idle>-0 [007] d... 671.401277: cpu_idle: state=4 cpu_id=7
> <idle>-0 [007] d... 671.404083: cpu_idle: state=4294967295 cpu_id=7
> kworker/7:2-556 [007] .... 671.404111: cpu_frequency: state=2900000 cpu_id=7
> <idle>-0 [007] d... 671.404125: cpu_idle: state=4 cpu_id=7
> <idle>-0 [007] d... 671.404974: cpu_idle: state=4294967295 cpu_id=7
> ...
> <idle>-0 [007] d... 671.501180: cpu_idle: state=4 cpu_id=7
> <idle>-0 [007] d... 671.995414: cpu_idle: state=4294967295 cpu_id=7
> kworker/7:2-556 [007] .... 671.995459: cpu_frequency: state=2800000 cpu_id=7
> <idle>-0 [007] d... 671.995469: cpu_idle: state=4 cpu_id=7
> <idle>-0 [007] d... 671.996287: cpu_idle: state=4294967295 cpu_id=7
> ...
> <idle>-0 [007] d... 672.001305: cpu_idle: state=4 cpu_id=7
> <idle>-0 [007] d... 672.078374: cpu_idle: state=4294967295 cpu_id=7
> kworker/7:2-556 [007] .... 672.078410: cpu_frequency: state=2600000 cpu_id=7
> <idle>-0 [007] d... 672.078419: cpu_idle: state=4 cpu_id=7
> <idle>-0 [007] d... 672.158020: cpu_idle: state=4294967295 cpu_id=7
> kworker/7:2-556 [007] .... 672.158040: cpu_frequency: state=2400000 cpu_id=7
> <idle>-0 [007] d... 672.158044: cpu_idle: state=4 cpu_id=7
> <idle>-0 [007] d... 672.160038: cpu_idle: state=4294967295 cpu_id=7
> ...
> <idle>-0 [007] d... 672.234557: cpu_idle: state=4 cpu_id=7
> <idle>-0 [007] d... 672.237121: cpu_idle: state=4294967295 cpu_id=7
> kworker/7:2-556 [007] .... 672.237174: cpu_frequency: state=2100000 cpu_id=7
> <idle>-0 [007] d... 672.237186: cpu_idle: state=4 cpu_id=7
> <idle>-0 [007] d... 672.237778: cpu_idle: state=4294967295 cpu_id=7
> ...
> <idle>-0 [007] d... 672.267902: cpu_idle: state=4 cpu_id=7
> <idle>-0 [007] d... 672.269860: cpu_idle: state=4294967295 cpu_id=7
> kworker/7:2-556 [007] .... 672.269906: cpu_frequency: state=1900000 cpu_id=7
> <idle>-0 [007] d... 672.269914: cpu_idle: state=4 cpu_id=7
> <idle>-0 [007] d... 672.271902: cpu_idle: state=4294967295 cpu_id=7
> ...
> <idle>-0 [007] d... 672.751342: cpu_idle: state=4 cpu_id=7
> <idle>-0 [007] d... 672.823056: cpu_idle: state=4294967295 cpu_id=7
> kworker/7:2-556 [007] .... 672.823095: cpu_frequency: state=1600000 cpu_id=7
>
> WITH
>
> <idle>-0 [007] dN.. 4380.928009: cpu_idle: state=4294967295 cpu_id=7
> kworker/7:2-399 [007] .... 4380.949767: cpu_frequency: state=2000000 cpu_id=7
> kworker/7:2-399 [007] .... 4380.969765: cpu_frequency: state=2200000 cpu_id=7
> kworker/7:2-399 [007] .... 4381.009766: cpu_frequency: state=2500000 cpu_id=7
> kworker/7:2-399 [007] .... 4381.029767: cpu_frequency: state=2600000 cpu_id=7
> kworker/7:2-399 [007] .... 4381.049769: cpu_frequency: state=2800000 cpu_id=7
> kworker/7:2-399 [007] .... 4381.069769: cpu_frequency: state=3000000 cpu_id=7
> kworker/7:2-399 [007] .... 4381.089771: cpu_frequency: state=3100000 cpu_id=7
> kworker/7:2-399 [007] .... 4381.109772: cpu_frequency: state=3400000 cpu_id=7
> kworker/7:2-399 [007] .... 4381.129773: cpu_frequency: state=3401000 cpu_id=7
> <idle>-0 [007] d... 4428.226159: cpu_idle: state=1 cpu_id=7
> <idle>-0 [007] d... 4428.226176: cpu_idle: state=4294967295 cpu_id=7
> <idle>-0 [007] d... 4428.226181: cpu_idle: state=4 cpu_id=7
> <idle>-0 [007] d... 4428.227177: cpu_idle: state=4294967295 cpu_id=7
> ...
> <idle>-0 [007] d... 4428.551640: cpu_idle: state=4 cpu_id=7
> <idle>-0 [007] d... 4428.649239: cpu_idle: state=4294967295 cpu_id=7
> kworker/7:2-399 [007] .... 4428.649268: cpu_frequency: state=2800000 cpu_id=7
> <idle>-0 [007] d... 4428.649278: cpu_idle: state=4 cpu_id=7
> <idle>-0 [007] d... 4428.689856: cpu_idle: state=4294967295 cpu_id=7
> ...
> <idle>-0 [007] d... 4428.799542: cpu_idle: state=4 cpu_id=7
> <idle>-0 [007] d... 4428.801683: cpu_idle: state=4294967295 cpu_id=7
> kworker/7:2-399 [007] .... 4428.801748: cpu_frequency: state=1700000 cpu_id=7
> <idle>-0 [007] d... 4428.801761: cpu_idle: state=4 cpu_id=7
> <idle>-0 [007] d... 4428.806545: cpu_idle: state=4294967295 cpu_id=7
> ...
> <idle>-0 [007] d... 4429.051880: cpu_idle: state=4 cpu_id=7
> <idle>-0 [007] d... 4429.086240: cpu_idle: state=4294967295 cpu_id=7
> kworker/7:2-399 [007] .... 4429.086293: cpu_frequency: state=1600000 cpu_id=7
>
> Without the patch the CPU dropped to min frequency after 3.2s
> With the patch applied the CPU dropped to min frequency after 0.86s
>
> Signed-off-by: Stratos Karafotis <stratosk@...aphore.gr>
> Acked-by: Viresh Kumar <viresh.kumar@...aro.org>
Applied.
Thanks,
Rafael
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