linux-kernel - Re: [PATCH] cpufreq: intel_pstate: Optimize IO boost in non HWP mode

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Date:   Mon, 3 Sep 2018 18:10:27 +0300
From:   Eero Tamminen <eero.t.tamminen@...el.com>
To:     Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        lenb@...nel.org, rjw@...ysocki.net, viresh.kumar@...aro.org
Cc:     mgorman@...hsingularity.net, currojerez@...eup.net,
        ggherdovich@...e.cz, peterz@...radead.org,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] cpufreq: intel_pstate: Optimize IO boost in non HWP mode

Hi,

On 31.08.2018 20:28, Srinivas Pandruvada wrote:
...
> As per testing Eero Tamminen, the results are comparable to the patchset
> https://patchwork.kernel.org/patch/10312259/
> But he has to watch results for several days to check trend.

It's close, but there is some gap compared to Francisco's version.

(Because of the large variance on TDP limited devices, and factors 
causing extra perf differences e.g. between boots, it's hard to give 
exact number without having trends from several days / weeks.  I would 
also need new version of Fransisco's patch set that applies to latest 
kernel like yours does.)

> Since here boost is getting limited to turbo and non turbo, we need some
> ways to adjust the fractions corresponding to max non turbo as well. It
> is much easier to use the actual P-state limits for boost instead of
> fractions. So here P-state io boost limit is applied on top of the
> P-state limit calculated via current algorithm by removing current
> io_wait boost calculation using fractions.
> 
> Since we prefer to use common algorithm for all processor platforms, this
> change was tested on other client and sever platforms as well. All results
> were within the margin of errors. Results:
> https://bugzilla.kernel.org/attachment.cgi?id=278149

Good.

Francisco, how well the listed PTS tests cover latency bound cases you 
were concerned about?  [1]

	- Eero

[1] Fransisco was concerned that the patch:
* trade-off might regress latency bound cases (which I haven't tested, I 
tested only 3D throughput), and
* that it addressed only other of the sources of energy inefficiencies 
he had identified (which could explain slightly better 3D results from 
his more complex patch set).