linux-kernel - Re: [PATCH 1/2] dt-bindings: cpufreq: Introduce QCOM CPUFREQ Firmware bindings

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Date:   Mon, 12 Nov 2018 16:28:56 -0800
From:   Matthias Kaehlcke <mka@...omium.org>
To:     Amit Kucheria <amit.kucheria@...aro.org>
Cc:     Taniya Das <tdas@...eaurora.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux PM list <linux-pm@...r.kernel.org>,
        Stephen Boyd <sboyd@...nel.org>,
        Rajendra Nayak <rnayak@...eaurora.org>,
        DTML <devicetree@...r.kernel.org>, Rob Herring <robh@...nel.org>,
        Saravana Kannan <skannan@...eaurora.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>, evgreen@...gle.com
Subject: Re: [PATCH 1/2] dt-bindings: cpufreq: Introduce QCOM CPUFREQ
 Firmware bindings

On Thu, Oct 25, 2018 at 03:43:39PM -0700, Matthias Kaehlcke wrote:
> Hi,
> 
> On Tue, Oct 23, 2018 at 05:23:34PM +0530, Amit Kucheria wrote:
> > Hi Taniya,
> > 
> > Both the patches are missing v9 in their subject line - this threw off
> > patchwork when trying to download the patches.
> > 
> > On Thu, Oct 11, 2018 at 5:06 PM Taniya Das <tdas@...eaurora.org> wrote:
> > >
> > > Add QCOM cpufreq firmware device bindings for Qualcomm Technology Inc's
> > > SoCs. This is required for managing the cpu frequency transitions which are
> > > controlled by the hardware engine.
> > 
> > I tested these patches on the sdm845-mtp against 4.19 and found that
> > the frequency gets stuck at the highest opp (the boost frequency)
> > after running a couple of 'yes > /dev/null &' instances. Have you
> > tested these against a mainline kernel?
> > 
> > See cpufreq statistics below:
> > 
> > linaro-test [rc=0]# cat policy?/scaling_cur_freq
> > 300000
> > 2803200
> > 
> > linaro-test [rc=0]# cat policy?/stats/time_in_state
> > 300000 100840
> > 403200 388
> > 480000 71
> > 576000 54
> > 652800 22
> > 748800 11
> > 825600 5
> > 902400 5
> > 979200 9
> > 1056000 3
> > 1132800 2
> > 1228800 5
> > 1324800 8
> > 1420800 2
> > 1516800 1
> > 1612800 0
> > 1689600 0
> > 1766400 392
> > 825600 22048
> > 902400 21
> > 979200 4
> > 1056000 15
> > 1209600 6
> > 1286400 0
> > 1363200 1
> > 1459200 0
> > 1536000 0
> > 1612800 1
> > 1689600 0
> > 1766400 0
> > 1843200 2
> > 1920000 2
> > 1996800 0
> > 2092800 0
> > 2169600 0
> > 2246400 0
> > 2323200 0
> > 2400000 0
> > 2476800 0
> > 2553600 0
> > 2649600 0
> > 2707200 0
> > 2764800 0
> > 2784000 0
> > 2803200 79718
> 
> I can repro this on SDM845 with a v4.19 kernel.
> 
> Since the little cores don't have a boost frequency I think maxing out
> can be expected with a high workload and no thermal throttling.
> However the big cores have a boost frequency (2.803 MHz), so the
> driver shouldn't be stuck at it. Though in practice I also wonder if
> the ~1% 'boost' makes a big difference in terms of performance or CPU
> overload ...

>From Documentation/cpu-freq/boost.txt:

"Some CPUs support a functionality to raise the operating frequency of
some cores in a multi-core package if certain conditions apply, mostly
if the whole chip is not fully utilized and below it's intended thermal
budget."

According to this it is not per se an issue that the cores are
operating at the boost frequency for a prolonged time. The use of the
highest frequency can be expected with a certain system load and
the/a boost frequency may be used unless a thermal or other conditions
prevents it.

I think the real question is: why is the last frequency automatically
considered a boost frequency? On (my) SDM845 it is only about 1%
higher than the previous one (2.803 GHz vs 2.784 GHz), that hardly
seems like a 'boost'.

Thanks

Matthias