linux-kernel - RE: [PATCH v4 1/6] x86,sched: Add support for frequency invariance

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Message-ID: <000001d5a368$9eece830$dcc6b890$@net>
Date:   Mon, 25 Nov 2019 00:16:15 -0800
From:   "Doug Smythies" <dsmythies@...us.net>
To:     "'Giovanni Gherdovich'" <ggherdovich@...e.cz>,
        "'Srinivas Pandruvada'" <srinivas.pandruvada@...ux.intel.com>,
        "'Thomas Gleixner'" <tglx@...utronix.de>,
        "'Ingo Molnar'" <mingo@...hat.com>,
        "'Peter Zijlstra'" <peterz@...radead.org>,
        "'Borislav Petkov'" <bp@...e.de>, "'Len Brown'" <lenb@...nel.org>,
        "'Rafael J . Wysocki'" <rjw@...ysocki.net>
Cc:     <x86@...nel.org>, <linux-pm@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        "'Mel Gorman'" <mgorman@...hsingularity.net>,
        "'Matt Fleming'" <matt@...eblueprint.co.uk>,
        "'Viresh Kumar'" <viresh.kumar@...aro.org>,
        "'Juri Lelli'" <juri.lelli@...hat.com>,
        "'Paul Turner'" <pjt@...gle.com>,
        "'Vincent Guittot'" <vincent.guittot@...aro.org>,
        "'Quentin Perret'" <qperret@...rret.net>,
        "'Dietmar Eggemann'" <dietmar.eggemann@....com>
Subject: RE: [PATCH v4 1/6] x86,sched: Add support for frequency invariance

On 2019.11.23 23:50 Doug Smythies wrote:

> Hi all,
>
> The address list here is likely incorrect,
> and this e-mail is really about a kernel 5.4
> bisected regression.
>
> It had been since mid September, and kernel 5.3-rc8 since
> I had tried this, so I wanted to try it again. Call it due diligence.
> I focused on my own version of the "gitsource" test.
>
> Kernel 5.4-rc8 (as a baseline reference).
>
> My results were extremely surprising.
>
> As it turns out, at least on my test computer, both the
> acpi-cpufreq and intel_cpufreq CPU frequency scaling drivers
> using the schedutil governor are broken. For the tests that
> I ran, there is negligible difference between them and the
> performance governor. So, one might argue that they are not
> broken, but rather working incredibly well, which if true
> then this patch is no longer needed.

Should be able to gain better insight here with the 
intel_pstate_tracer.py utility, watching for differences
in rates of rotation between CPUs. Too late tonight.

>
> I bisected the kernel and got:
>
> first bad commit: [04cbfba6208592999d7bfe6609ec01dc3fde73f5]
> Merge tag 'dmaengine-5.4-rc1' of git://git.infradead.org/users/vkoul/slave-dma
>
> Which did not make any sense at all. I don't even know how
> this is being pulled into my kernel compile.
> O.K., I often (usually) make a mistake
> during bisection, so I did it again, and got the same result.
>
> Relevant excerpt from the commit:
>
> diff --cc drivers/dma/Kconfig
> index 413efef,03fa0c5..7c511e3
> --- a/drivers/dma/Kconfig
> +++ b/drivers/dma/Kconfig
> @@@ -294,8 -294,8 +294,8 @@@ config INTEL_IOATDM
>          If unsure, say N.
>
>  config INTEL_IOP_ADMA
>  -      tristate "Intel IOP ADMA support"
>  -      depends on ARCH_IOP32X || ARCH_IOP33X || ARCH_IOP13XX
>  +      tristate "Intel IOP32x ADMA support"
> -       depends on ARCH_IOP32X
> ++      depends on ARCH_IOP32X || COMPILE_TEST
>         select DMA_ENGINE
>         select ASYNC_TX_ENABLE_CHANNEL_SWITCH
>         help
>
> If I revert the above, manually, then everything behaves
> as expected (minimally tested only, so far).
>
> Are others seeing the schedutil governors not working as
> expected with any of kernels 5.4-rc1 - 5.4-rc8?
>
> I do have a pretty graph of my method of doing the
> "gitsource" test, but am not ready to post it yet.

Graphs and write up (mostly the same as herein) are now
here:

http://www.smythies.com/~doug/linux/single-threaded/k54regression/index.html

The graphs are rather crowded, sorry.

> Here is some gitsource test data, 6 runs of "make test",
> the first run is discarded:
>
> "gg 6" means this 6 patch set.
>
> Kernel 5.4-rc8 + revert, intel_cpufreq/schedutil: 3899 seconds
> Kernel 5.4-rc8 + gg 6 + revert, intel_cpufreq/schedutil: 2740.7 seconds
> Ratio: 0.70 (as expected)

Kernel 5.4-rc8 + gg 6 + revert, forced CPU affinity performance: 2106.5 seconds

> Kernel 5.4-rc8, intel_cpufreq/schedutil: 2334.7 seconds (faster than expected)
> Kernel 5.4-rc8 + gg 6 patch set, intel_cpufreq/schedutil: 2275.0 seconds (faster than expected)
> Ratio: 0.97 (not as expected)
> Kernel 5.4-rc8, intel_cpufreq/performance: 2215.3 seconds
> Kernel 5.4-rc8, intel_cpufreq/ondemand: 3286.3 seconds
> Re-stated from previous e-mail:
> Kernel 5.3-rc8, intel_cpufreq/schedutil: ratio: 0.69 (I don't have the original times)

... Doug