linux-kernel - RE: [RFC/RFT][PATCH v3] cpuidle: New timer events oriented governor for tickless systems

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Date:   Sat, 10 Nov 2018 13:47:33 -0800
From:   "Doug Smythies" <dsmythies@...us.net>
To:     "'Rafael J. Wysocki'" <rjw@...ysocki.net>
Cc:     "'Srinivas Pandruvada'" <srinivas.pandruvada@...ux.intel.com>,
        "'Peter Zijlstra'" <peterz@...radead.org>,
        "'LKML'" <linux-kernel@...r.kernel.org>,
        "'Frederic Weisbecker'" <frederic@...nel.org>,
        "'Mel Gorman'" <mgorman@...e.de>,
        "'Daniel Lezcano'" <daniel.lezcano@...aro.org>,
        "'Linux PM'" <linux-pm@...r.kernel.org>,
        "'Doug Smythies'" <dsmythies@...us.net>,
        "'Giovanni Gherdovich'" <ggherdovich@...e.cz>
Subject: RE: [RFC/RFT][PATCH v3] cpuidle: New timer events oriented governor for tickless systems

On 2018.11.07 09:04 Doug Smythies wrote:

> The Phoronix dbench test was run under the option to run all
> the tests, instead of just one number of clients. This was done
> with a reference/baseline kernel of 4.20-rc1, and also with this
> TEO version 3 patch. The tests were also repeated with trace
> enabled for 5000 seconds. Idle information and processor
> package power were sampled once per minute in all test runs.
>
> The results are:
> http://fast.smythies.com/linux-pm/k420/k420-dbench-teo3.htm
> http://fast.smythies.com/linux-pm/k420/histo_compare.htm

Another observation from the data, and for the reference/
baseline 4.20-rc1 kernel, idle state 0 histogram plots
is that there are several (280) long idle durations.

For unknown reasons, these are consistently dominated by
CPU 5 on my system (264 of the 280, in this case).

No other test that I have tried shows this issue,
But other tests also tend to set the need_resched
flag whereas the dbench test doesn't.

Older kernels also have the issue. I tried: 4.19, 4.18
4.17, 4.16+"V9" idle re-work patch set of the time.
There is no use going back further, because "V9" was
to address excessively long durations in shallow idle states.

I have not made progress towards determining the root issue.

... Doug