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:   Wed, 10 Feb 2021 09:34:07 -0800
From:   nnet <nnet@...tmail.fm>
To:     Pali Rohár <pali@...nel.org>
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 Wed, Feb 10, 2021, at 1:23 AM, Pali Rohár wrote:
> On Tuesday 09 February 2021 18:07:41 nnet wrote:
> > On Tue, Feb 9, 2021, at 5:51 PM, nnet wrote:
> > > On Tue, Feb 9, 2021, at 5:31 PM, nnet wrote:
> > > > On Tue, Feb 9, 2021, at 3:26 PM, Marek Behún wrote:
> > > > > On Tue, 09 Feb 2021 15:16:45 -0800
> > > > > nnet <nnet@...tmail.fm> wrote:
> > > > > 
> > > > > > I've two of these and I've just swapped them (and re-pasted the heat sinks).
> > > > > > 
> > > > > > The second one ran under load for awhile and now has frozen as well.
> > > > > > 
> > > > > > Under a moderate load `wget -O /dev/null <large.bin>` @X00Mbits they are fine.
> > > > > > 
> > > > > > Under a 1 min speed test of load ~200Mbits routed WireGuard they freeze.
> > > > > > 
> > > > > > They fine with both those workloads @1000_800.
> > > > > > 
> > > > > > Perhaps it's heat? Unfortunately I don't have any numbers on that ATM.
> > > > > 
> > > > > Try disabling cpufreq in kernel completely, compile boot image at
> > > > > 1200 MHz. If it continues freezing, then I fear we can't help you with
> > > > > 1200 MHz :(
> > > > 
> > > > cat /sys/devices/system/cpu/cpufreq/policy0/scaling_available_frequencies 
> > > > 200000 300000 600000 1200000 
> > > > 
> > > > I'm not getting any freezes with 1.2GHz fixed after 20 minutes of load:
> > > > 
> > > > echo 1200000 > /sys/devices/system/cpu/cpufreq/policy0/scaling_min_freq
> > > > 
> > > > Setting it back to min 200MHz I get a freeze within a minute:
> > > > 
> > > > echo 200000 > /sys/devices/system/cpu/cpufreq/policy0/scaling_min_freq
> 
> 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.

>> Update the CPU voltage value for loads L0 and L1 accordingly when base
>> frequency is 1000 or 1200 MHz. The minimal value is updated from the
>> original 1.05V to 1.108V.

Perhaps similiar to how a minimum of 1108 mV is useful when shifting to 1GHz, using a minimum of 1132 is useful when shifting to 1.2GHz.

> (of course on 1.2 GHz variant you need to adjust values as only
> following frequencies 200000 300000 600000 1200000 are supported)
> 
> > > > > Marek
> > > > >
> > > 
> > > > +#define MIN_VOLT_MV_FOR_L0_L1_1GHZ 1108
> > > 
> > > Based on the below at boot time might an equivalent of the above need 
> > > to be 1225 for 1.2GHz?
> > > 
> > > 1200_750
> > > SVC REV: 5, CPU VDD voltage: 1.225V
> > > 
> > > 1000_800
> > > SVC REV: 5, CPU VDD voltage: 1.108V
> 
> This value is printed in WTMI avs.c by following code:
> 
>     shift = OTP_SVC_SPEED_1000_OFF;
>     (OR)
>     shift = OTP_SVC_SPEED_1200_OFF;
> 
>     vdd_otp = ((otp_data[OTP_DATA_SVC_SPEED_ID] >> shift) +
>                 AVS_VDD_BASE) & AVS_VDD_MASK;
>     regval |= (vdd_otp << HIGH_VDD_LIMIT_OFF);
>     regval |= (vdd_otp << LOW_VDD_LIMIT_OFF);
>     printf("SVC REV: %d, CPU VDD voltage: %s\n", svc_rev,
>             avis_dump[vdd_otp].desc);
> 
> So voltage value is read from the OTP memory.
> 
> But I do not know what this value means.
> 
> > I did this for a quick test for 1.2GHz:
> > 
> > +#define MIN_VOLT_MV_FOR_L0_L1_1GHZ 1225
> > 
> > This is working well so far. Frequency is shifting up/down with load applied/stopped.
>