Re: [PATCH 18/19] target/ppc/pmu_book3s_helper.c: add PM_CMPLU_STALL mock events

[David Gibson]

On Tue, Aug 10, 2021 at 04:48:59PM -0300, Daniel Henrique Barboza wrote:
> 
> 
> On 8/10/21 1:17 AM, David Gibson wrote:
> > On Mon, Aug 09, 2021 at 10:10:56AM -0300, Daniel Henrique Barboza wrote:
> > > EBB powerpc kernel test 'multi_counter_test' uses PM_CMPLU_STALL events
> > > that we do not support. These events are related to CPU stalled/wasted
> > > cycles while waiting for resources, cache misses and so on.
> > > 
> > > Unlike the 0xFA event added previously, there's no available equivalent
> > > for us to use, and at this moment we can't sample those events as well.
> > > What we can do is mock those events as if we were calculating them.
> > > 
> > > This patch implements PM_CMPLU_STALL, PM_CMPLU_STALL_FXU,
> > > PM_CMPLU_STALL_OTHER_CMPL and PM_CMPLU_STALL_THRD mock events by giving
> > > them a fixed amount of the total elapsed cycles.
> > > 
> > > The chosen sample values for these events (25% of total cycles for
> > > PM_CMPLU_STALL and 5% for the other three) were chosen at random and has
> > > no intention of being truthful with what a real PowerPC hardware would
> > > give us. Our intention here is to make 'multi_counter_test' EBB test
> > > pass.
> > 
> > Hmm.  I guess these mock values make sense for getting the kernel
> > tests to pass, but I'm not sure if it's a good idea in general.  Would
> > we be better off just reporting 0 always - that would be a strong hint
> > to someone attempting to analyze results that something is fishy (in
> > this case that they don't actually have a real CPU).
> 
> We can drop this patch and I'll add a note in the docs that the EBB kernel
> test 'multi_counter_test' fails because the PMU does not implement STALL
> events.

Sounds good for now.  We can reconsider this if we have a specific
justification for it.

-- 
David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!
http://www.ozlabs.org/~dgibson

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