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

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Message-ID: <CAJZ5v0gu=rALS9ZLNMDT3cw_sT2m8XCKP6+AW3488x2Q9EXM3g@mail.gmail.com>
Date:   Tue, 1 Oct 2019 11:31:32 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Doug Smythies <dsmythies@...us.net>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        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 Sun, Sep 29, 2019 at 6:05 PM Doug Smythies <dsmythies@...us.net> wrote:
>
> 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.

Thanks for this work!

Please also note that there is a teo patch in 5.4-rc1 that may make a
difference in principle.