Hey,
Some test results:
On Thursday 18 Feb 2021 at 16:35:38 (+0000), Ionela Voinescu wrote:
[..]
> > +static void __init cppc_freq_invariance_init(void)
> > +{
[..]
> > +
> > + ret = cppc_get_perf_ctrs(i, &fb_ctrs);
> > + if (!ret)
> > + per_cpu(cppc_fi->prev_perf_fb_ctrs, i) = fb_ctrs;
>
After fixing this one:
cppc_fi->prev_perf_fb_ctrs = fb_ctrs;
I got the following:
Platform:
- Juno R2 (CPUs [0-3] are littles, CPUs [4-5] are bigs)
+ PMU counters, used by CPPC through FFH
+ userspace/schedutil
- Verifying that with userspace governor we see a correct change in
scale factor:
root@buildroot:~# dmesg | grep FIE
[ 6.436770] AMU: CPUs[0-3]: AMU counters WON'T be used for FIE.
[ 6.436962] AMU: CPUs[4-5]: AMU counters WON'T be used for FIE.
[ 6.451510] CPPC:CPUs[0-5]: CPPC counters will be used for FIE.
root@buildroot:~# echo 600000 > policy4/scaling_setspeed
[ 353.939495] CPU4: Invariance(cppc) scale: 512.
[ 353.939497] CPU5: Invariance(cppc) scale: 512.
root@buildroot:~# echo 1200000 > policy4/scaling_setspeed
[ 372.683511] CPU5: Invariance(cppc) scale: 1024.
[ 372.683518] CPU4: Invariance(cppc) scale: 1024.
root@buildroot:~# echo 450000 > policy0/scaling_setspeed
[ 641.495513] CPU2: Invariance(cppc) scale: 485.
[ 641.495514] CPU1: Invariance(cppc) scale: 485.
[ 641.495517] CPU0: Invariance(cppc) scale: 485.
[ 641.495542] CPU3: Invariance(cppc) scale: 485.
root@buildroot:~# echo 950000 > policy0/scaling_setspeed
[ 852.015514] CPU2: Invariance(cppc) scale: 1024.
[ 852.015514] CPU1: Invariance(cppc) scale: 1024.
[ 852.015517] CPU0: Invariance(cppc) scale: 1024.
[ 852.015541] CPU3: Invariance(cppc) scale: 1024.
- I ran some benchmarks as well (perf, hackbench, dhrystone) on the same
platform, using the userspace governor at fixed frequency, to evaluate
the impact of the work we do or don't do on the tick.
./perf bench sched pipe
(10 iterations, higher is better, ops/s, comparisons with
cpufreq-based FIE)
cpufreq-based FIE AMU-based FIE CPPC-based FIE
----------------------------------------------------
39498.8 40984.7 38893.4
std: 3.766% std: 4.461% std: 0.575%
diff: 3.625% diff: -1.556%
./hackbench -l 1000
(10 iterations, lower is better, seconds, comparison with
cpufreq-based FIE)
cpufreq-based FIE AMU-based FIE CPPC-based FIE
----------------------------------------------------
6.4207 6.3386 6.7841
std: 7.298% std: 2.252% std: 2.460%
diff: -1.295% diff: 5.356%
This shows a small regression for the CPPC-based FIE, but within the
standard deviation.
I ran some dhrystone benchmarks (./dhrystone -t 2/34/5/6/ -l 5000) as
well with schedutil governor to understand if an increase in accuracy
with the AMU/CPPC counters makes a difference. Given the
characteristics of the platform it's no surprise that the results
were very similar between the three cases, so I won't bore you with
the numbers.
Hope it helps,
Ionela.
