[PATCH V3 2/2] cpufreq: cppc: Add support for frequency invariance

[Viresh Kumar]

On 22-02-21, 11:00, Ionela Voinescu wrote:
> Hey,
> 
> Some test results:

Nice, I haven't responded earlier as Vincent was also testing the
stuff out later last week and was planning to do it more this week.

> 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;

Yeah, I already fixed it and made several changes based on your
feedback.

> 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 at 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 at buildroot:~# echo 600000 > policy4/scaling_setspeed
> 	[  353.939495] CPU4: Invariance(cppc) scale: 512.
> 	[  353.939497] CPU5: Invariance(cppc) scale: 512.
> 
> 	root at buildroot:~# echo 1200000 > policy4/scaling_setspeed
> 	[  372.683511] CPU5: Invariance(cppc) scale: 1024.
> 	[  372.683518] CPU4: Invariance(cppc) scale: 1024.
> 
> 	root at 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 at 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.

Great.

>  - 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.

Nice, I have much more confidence on this stuff now :)

Thanks a lot Ionela, I will resend the series again today then.

-- 
viresh