linux-kernel - Re: [PATCH v1 6/7] arm64: dts: sdm845: Increase alert trip point to 95 degrees

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Message-ID: <20190110021522.GW261387@google.com>
Date:   Wed, 9 Jan 2019 18:15:22 -0800
From:   Matthias Kaehlcke <mka@...omium.org>
To:     Amit Kucheria <amit.kucheria@...aro.org>
Cc:     linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        bjorn.andersson@...aro.org, viresh.kumar@...aro.org,
        edubezval@...il.com, andy.gross@...aro.org, tdas@...eaurora.org,
        swboyd@...omium.org, dianders@...omium.org,
        David Brown <david.brown@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>
Subject: Re: [PATCH v1 6/7] arm64: dts: sdm845: Increase alert trip point to
 95 degrees

On Wed, Jan 09, 2019 at 05:15:33PM -0800, Matthias Kaehlcke wrote:
> Hi Amit,
> 
> On Thu, Jan 10, 2019 at 05:30:55AM +0530, Amit Kucheria wrote:
> > 75 degrees is too aggressive for throttling the CPU. After speaking to
> > Qualcomm engineers, increase it to 95 degrees.
> > 
> > Signed-off-by: Amit Kucheria <amit.kucheria@...aro.org>
> > ---
> >  arch/arm64/boot/dts/qcom/sdm845.dtsi | 16 ++++++++--------
> >  1 file changed, 8 insertions(+), 8 deletions(-)
> > 
> > diff --git a/arch/arm64/boot/dts/qcom/sdm845.dtsi b/arch/arm64/boot/dts/qcom/sdm845.dtsi
> > index c27cbd3bcb0a..29e823b0caf4 100644
> > --- a/arch/arm64/boot/dts/qcom/sdm845.dtsi
> > +++ b/arch/arm64/boot/dts/qcom/sdm845.dtsi
> > @@ -1692,7 +1692,7 @@
> >  
> >  			trips {
> >  				cpu_alert0: trip0 {
> > -					temperature = <75000>;
> > +					temperature = <95000>;
> >  					hysteresis = <2000>;
> >  					type = "passive";
> >  				};
> > @@ -1713,7 +1713,7 @@
> >  
> >  			trips {
> >  				cpu_alert1: trip0 {
> > -					temperature = <75000>;
> > +					temperature = <95000>;
> >  					hysteresis = <2000>;
> >  					type = "passive";
> >  				};
> > @@ -1734,7 +1734,7 @@
> >  
> >  			trips {
> >  				cpu_alert2: trip0 {
> > -					temperature = <75000>;
> > +					temperature = <95000>;
> >  					hysteresis = <2000>;
> >  					type = "passive";
> >  				};
> > @@ -1755,7 +1755,7 @@
> >  
> >  			trips {
> >  				cpu_alert3: trip0 {
> > -					temperature = <75000>;
> > +					temperature = <95000>;
> >  					hysteresis = <2000>;
> >  					type = "passive";
> >  				};
> > @@ -1776,7 +1776,7 @@
> >  
> >  			trips {
> >  				cpu_alert4: trip0 {
> > -					temperature = <75000>;
> > +					temperature = <95000>;
> >  					hysteresis = <2000>;
> >  					type = "passive";
> >  				};
> > @@ -1797,7 +1797,7 @@
> >  
> >  			trips {
> >  				cpu_alert5: trip0 {
> > -					temperature = <75000>;
> > +					temperature = <95000>;
> >  					hysteresis = <2000>;
> >  					type = "passive";
> >  				};
> > @@ -1818,7 +1818,7 @@
> >  
> >  			trips {
> >  				cpu_alert6: trip0 {
> > -					temperature = <75000>;
> > +					temperature = <95000>;
> >  					hysteresis = <2000>;
> >  					type = "passive";
> >  				};
> > @@ -1839,7 +1839,7 @@
> >  
> >  			trips {
> >  				cpu_alert7: trip0 {
> > -					temperature = <75000>;
> > +					temperature = <95000>;
> >  					hysteresis = <2000>;
> >  					type = "passive";
> >  				};
> 
> The change itself looks good to me, however I wonder if it would be
> worth to eliminate redundancy and merge the current 8 thermal zones
> into 2, one for the Silver and one for the Gold cluster (as done by
> http://crrev.com/c/1381752). There is a single cooling device for
> each cluster, so it's not clear to me if there is any gain from having
> a separate thermal zone for each CPU. If it is important to monitor
> the temperatures of the individual cores this can still be done by
> configuring the thermal zone of the cluster with multiple thermal
> sensors.

I see your idea is to have a cooling device per CPU ("arm64: dts:
sdm845: wireup the thermal trip points to cpufreq" /
https://lore.kernel.org/patchwork/patch/1030742/), however that
doesn't work as intended. Only two cpufreq 'devices' are created,
one for CPU0 and one for CPU4. In consequence cpufreq->ready() only
runs for these cores and only two cooling devices are
registered. Since the cores of a cluster all run at the same
frequency I also doubt if having multiple cooling devices would
bring any benefits.

Cheers

Matthias