linux-kernel - RE: [RFC/RFT][PATCH v8] cpuidle: New timer events oriented governor for tickless systems

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Date:   Sun, 29 Sep 2019 09:04:56 -0700
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>,
        "'Chen, Hu'" <hu1.chen@...el.com>,
        "'Quentin Perret'" <quentin.perret@....com>,
        "'Linux PM'" <linux-pm@...r.kernel.org>,
        "'Giovanni Gherdovich'" <ggherdovich@...e.cz>
Subject: RE: [RFC/RFT][PATCH v8] cpuidle: New timer events oriented governor for tickless systems

On 2019.09.26 09:32 Doug Smythies wrote:

> If the deepest idle state is disabled, the system
> can become somewhat unstable, with anywhere between no problem
> at all, to the occasional temporary jump using a lot more
> power for a few seconds, to a permanent jump using a lot more
> power continuously. I have been unable to isolate the exact
> test load conditions under which this will occur. However,
> temporarily disabling and then enabling other idle states
> seems to make for a somewhat repeatable test. It is important
> to note that the issue occurs with only ever disabling the deepest
> idle state, just not reliably.
>
> I want to know how you want to proceed before I do a bunch of
> regression testing.

I did some regression testing anyhow, more to create and debug
a methodology than anything else.

> On 2018.12.11 03:50 Rafael J. Wysocki wrote:
>
>> v7 -> v8:
>>  * Apply the selection rules to the idle deepest state as well as to
>>    the shallower ones (the deepest idle state was treated differently
>>    before by mistake).
>>  * Subtract 1/2 of the exit latency from the measured idle duration
>>    in teo_update() (instead of subtracting the entire exit latency).
>>    This makes the idle state selection be slightly more performance-
>>   oriented.
>
> I have isolated the issue to a subset of the v7 to v8 changes, however
> it was not the exit latency changes.
>
> The partial revert to V7 changes I made were (on top of 5.3):

The further testing showed a problem or two with my partial teo-v7 reversion
(I call it teo-v12) under slightly different testing conditions.

I also have a 5.3 based kernel with the current teo reverted and the entire
teo-v7 put in its place. I have yet to find a idle state disabled related issue
with this kernel.

I'll come back to this thread at a later date with better details and test results.

... Doug