Re: [EXTERNAL] Re: [PATCH v2 8/8] arm64: dts: allwinner: h616: enable DVFS for all boards

[Andre Przywara <andre.przywara@arm.com>]

On Tue, 19 Mar 2024 00:41:33 +0530
Amit Singh Tomar <amitsinght@marvell.com> wrote:

Hi,

> >>
> >> With the DT bindings now describing the format of the CPU OPP tables, we can include the OPP table in each board's .dts file, and specify the CPU power supply.
> >> This allows to enable DVFS, and get up to 50% of performance benefit in the highest OPP, or up to 60% power savings in the lowest OPP, compared to the fixed 1GHz @ 1.0V OPP we are running in by default
> >> at the moment.
> >> [Amit] Could you please elaborate, what test were run to see 50 % performance benefits?  
> > 
> > Currently all H616 boards running mainline firmware and kernels run at a
> > fixed 1GHz CPU clock frequency. If you happen to have a good SoC (bin 1 or
> > 3), this patchset will allow you to run at 1.5 GHz, which is 50% faster.
> > So anything that scales with CPU frequency should run much quicker.
> >   
> Okay, it would be interesting to see results of some benchmark here.

But why? This is not a performance optimisation, it's adding a missing
feature, because the CPU was locked to 1 GHz before, for safety
reasons, due to missing thermal and DVFS capability. Now it's able to
run at up to 1.5 GHz, as specified.
If you are upset about the bold claim, I can just remove it from the
commit message, it was just a heads up that we were leaving a lot of
performance on the table at the moment.

Posting absolute performance numbers is a tricky subject, legally, so
please run your own: http://www.netlib.org/benchmark/linpackc.new
$ musl-gcc -s -static -Ofast -o linpack linpack.c -lm -march=native -fno-math-errno -funsafe-math-optimizations
$ gcc --version
gcc (Debian 12.2.0-14) 12.2.0
# echo userspace > /sys/devices/system/cpu/cpufreq/policy0/scaling_governor
# echo 1008000 > /sys/devices/system/cpu/cpufreq/policy0/scaling_setspeed
$ ./linpack
# echo performance > /sys/devices/system/cpu/cpufreq/policy0/scaling_governor
$ ./linpack
$ dc -e '3k $high $low /p'
1.498

Cheers,
Andre