Re: [PATCH v2 3/3] PM / EM: Skip inefficient OPPs

[Lukasz Luba]

On 5/25/21 10:46 AM, Vincent Donnefort wrote:
> On Tue, May 25, 2021 at 09:33:01AM +0000, Quentin Perret wrote:
> > On Friday 21 May 2021 at 17:54:24 (+0100), Vincent Donnefort wrote:
> > > @@ -161,6 +162,8 @@ static int em_create_perf_table(struct device *dev, struct em_perf_domain *pd,
> > >   		table[i].cost = div64_u64(fmax * table[i].power,
> > >   					  table[i].frequency);
> > >   		if (table[i].cost >= prev_cost) {
> > > +			table[i].flags = EM_PERF_STATE_INEFFICIENT;
> > > +			pd->flags |= EM_PERF_DOMAIN_INEFFICIENCIES;
> >
> > If we're looking for micro-optimizations, then perhaps you could store
> > the index of the next efficient OPP (which would be 'i' if the current
> > OPP is already efficient), so you can jump to it directly when doing the
> > search.
>
> Wouldn't add any new field compared to this version so yeah might be an
> interesting improvement.

That's a few more instructions to parse the 'flags' filed. I'm not sure
if that brings speed improvements vs. if we not parse and have bool
filed with a simple looping. The out-of-order core might even suffer
from this parsing and loop index manipulations...