linux-kernel - Re: [PATCH mvebu v2 00/10] Armada 37xx: Fix cpufreq changing base CPU speed to 800 MHz from 1000 MHz

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Date:   Fri, 12 Feb 2021 00:44:45 +0100
From:   Pali Rohár <pali@...nel.org>
To:     nnet <nnet@...tmail.fm>
Cc:     Marek Behún <kabel@...nel.org>, a.heider@...il.com,
        andrew@...n.ch, gerald@....net, gregory.clement@...tlin.com,
        kostap@...vell.com, linux-arm-kernel@...ts.infradead.org,
        linux-clk@...r.kernel.org, linux-kernel@...r.kernel.org,
        luka.perkov@...tura.hr, miquel.raynal@...tlin.com,
        mturquette@...libre.com, rmk+kernel@...linux.org.uk,
        sboyd@...nel.org, tmn505@...il.com, vladimir.vid@...tura.hr
Subject: Re: [PATCH mvebu v2 00/10] Armada 37xx: Fix cpufreq changing base
 CPU speed to 800 MHz from 1000 MHz

On Thursday 11 February 2021 12:22:52 nnet wrote:
> On Thu, Feb 11, 2021, at 11:55 AM, Pali Rohár wrote:
> > On Wednesday 10 February 2021 11:08:59 nnet wrote:
> > > On Wed, Feb 10, 2021, at 10:03 AM, Pali Rohár wrote:
> > > > > > Hello! Could you please enable userspace governor during kernel
> > > > > > compilation?
> > > > > > 
> > > > > >     CONFIG_CPU_FREQ_GOV_USERSPACE=y
> > > > > > 
> > > > > > It can be activated via command:
> > > > > > 
> > > > > >     echo userspace > /sys/devices/system/cpu/cpufreq/policy0/scaling_governor
> > > > > > 
> > > > > > After that you can "force" CPU frequency to specific value, e.g.:
> > > > > > 
> > > > > >     echo 1000000 > /sys/devices/system/cpu/cpufreq/policy0/scaling_setspeed
> > > > > > 
> > > > > > I need to know which switch (from --> to freq) cause this system hang.
> > > > > > 
> > > > > > This patch series (via MIN_VOLT_MV_FOR_L0_L1_1GHZ) is fixing only
> > > > > > switching from 500 MHz to 1000 MHz on 1 GHz variant. As only this switch
> > > > > > is causing issue.
> > > > > > 
> > > > > > I have used following simple bash script to check that switching between
> > > > > > 500 MHz and 1 GHz is stable:
> > > > > > 
> > > > > >     while true; do
> > > > > >         echo 1000000 > /sys/devices/system/cpu/cpufreq/policy0/scaling_setspeed;
> > > > > >         echo 500000 > /sys/devices/system/cpu/cpufreq/policy0/scaling_setspeed;
> > > > > >         echo 1000000 > /sys/devices/system/cpu/cpufreq/policy0/scaling_setspeed;
> > > > > >         echo 500000 > /sys/devices/system/cpu/cpufreq/policy0/scaling_setspeed;
> > > > > >     done
> > > > > 
> > > > > echo userspace | tee /sys/devices/system/cpu/cpufreq/policy0/scaling_governor
> > > > > while true; do
> > > > >   echo 1200000 | tee /sys/devices/system/cpu/cpufreq/policy0/scaling_setspeed;
> > > > >   echo 600000 | tee /sys/devices/system/cpu/cpufreq/policy0/scaling_setspeed;
> > > > > done
> > > > > 
> > > > > >> +#define MIN_VOLT_MV_FOR_L0_L1_1GHZ 1108
> > > > > 
> > > > > With 1108 I get a freeze within a minute. The last output to stdout is 600000.
> > > > > 
> > > > > With 1120 it takes a few minutes.
> > > > > 
> > > > > With any of 1225, 1155, 1132 the device doesn't freeze over the full 5 minute load test.
> > > > > 
> > > > > I'm using ondemand now with the above at 1132 without issue so far.
> > > > 
> > > > Great, thank you for testing!
> > > > 
> > > > Can you check if switching between any two lower frequencies 200000
> > > > 300000 600000 is stable?
> > > 
> > > This is stable using 1132 mV for MIN_VOLT_MV_FOR_L0_L1_1GHZ:
> > > 
> > > while true; do
> > >   # down
> > >   echo 1200000 | tee /sys/devices/system/cpu/cpufreq/policy0/scaling_setspeed;
> > ...
> > 
> > Hello!
> > 
> > Could you please re-run test without tee, in form as I have shown above?
> > UART is slow and printing something to console adds delay which decrease
> > probability that real issue is triggered as this is timing issue.
> 
> The test was done over SSH.

Ok! But it is still better to not print any results as it adds unwanted
delay between frequency switching.

> > Also please do tests just between two frequencies in loop as I observed
> > that switching between more decreased probability to hit issue.
> 
> > > > > echo userspace | tee /sys/devices/system/cpu/cpufreq/policy0/scaling_governor
> > > > > while true; do
> > > > >   echo 1200000 | tee /sys/devices/system/cpu/cpufreq/policy0/scaling_setspeed;
> > > > >   echo 600000 | tee /sys/devices/system/cpu/cpufreq/policy0/scaling_setspeed;
> > > > > done
> 
> The first test ^ switched between 600 MHz and 1.2 GHz.
> 
> > The real issue for 1 GHz variant of A3720 is only when doing switch from
> > 500 MHz to 1 GHz. So could you try to do some tests also without
> > changing MIN_VOLT_MV_FOR_L0_L1_1GHZ and switching just between non-1.2
> > frequencies (to verify that on 1.2 GHz variant it is also from 600 MHz
> > to 1.2 GHz)?
> 
> With 1108 mV and switching between 600 MHz and 1.2GHz, I always saw a freeze within a minute.

I mean to try switching with 1.108 V between 200 MHz and 300 MHz or
between 300 MHz and 600 MHz. To check that issue is really only with
switch from 600 MHz to 1.2 GHz.

I need to know if current settings are fine for 200, 300 and 600 MHz
frequencies and the only 600 --> 1200 needs to be fixed.