Hi guys,

On Tuesday 04 Aug 2020 at 12:00:46 (+0530), Viresh Kumar wrote:

On 30-07-20, 12:29, Dietmar Eggemann wrote:

quoted

On 30/07/2020 06:24, Viresh Kumar wrote:

quoted

On 22-07-20, 10:37, Ionela Voinescu wrote:

quoted

+++ b/drivers/base/arch_topology.c

@@ -27,6 +27,7 @@ __weak bool arch_freq_counters_available(struct cpumask *cpus)
 }
 DEFINE_PER_CPU(unsigned long, freq_scale) = SCHED_CAPACITY_SCALE;
 
+#ifndef CONFIG_BL_SWITCHER
 void arch_set_freq_scale(struct cpumask *cpus, unsigned long cur_freq,
 			 unsigned long max_freq)
 {

@@ -46,6 +47,7 @@ void arch_set_freq_scale(struct cpumask *cpus, unsigned long cur_freq,
 	for_each_cpu(i, cpus)
 		per_cpu(freq_scale, i) = scale;
 }
+#endif

I don't really like this change, the ifdef hackery is disgusting and
then we are putting that in a completely different part of the kernel.

There are at least these two ways of solving this, maybe more:

- Fix the bl switcher driver and add the complexity in it (which you
  tried to do earlier).

- Add a cpufreq flag to skip arch-set-freq-scale call.

I agree it's not nice but IMHO the cpufreq flag is worse since we would
introduce new infrastructure only for a deprecated feature. I'm assuming
that BL SWITCHER is the only feature needing this CPUfreq flag extension.

#ifdef CONFIG_BL_SWITCHER is already in drivers/irqchip/irq-gic.c so
it's ugly already.

Runtime detecting (via bL_switching_enabled) of BL SWITCHER is right now
also only handled inside vexpress-spc-cpufreq.c via a
bL_switcher_notifier. A mechanism which also sits behind a #ifdef
CONFIG_BL_SWITCHER.

Vexpress one is a driver and so ugliness could be ignored here :)

So here is option number 3 (in continuation of the earlier two
options):
- Don't do anything for bL switcher, just add a TODO/NOTE in the
  driver that FIE is broken for switcher. And I don't think anyone
  will care about FIE for the switcher anyway :)

I gave it a bit of time in case anyone had strong opinions about this,
but given the lack of those, what I can do in this series is the
following: ignore the problem :). This issue was there before these
patches and it will continue to be there after these patches - nothing
changes.

Separately from this series, I can submit a patch with Viresh's
suggestion above and we can spin around a bit discussing this, if there
is interest. My opinion on this is that option 1 is ugly but it does fix
an issue in a relatively non-invasive way. I agree with "I don't think
anyone will care about FIE for the switcher anyway", but for me this
means that nobody will care if it's supported (and therefore option 1
is the proper solution). But if bL switcher is used, I think people might
care if it's broken, as it results in incorrect scheduler signals.
Therefore, I would not like leaving it broken (option 3). If it's not
used, option 2 is obvious.


Many thanks,
Ionela.

-- 
viresh

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