Messages in this thread | | | Date | Wed, 26 May 2021 14:49:22 +0100 | From | Vincent Donnefort <> | Subject | Re: [PATCH v2 0/3] EM / PM: Inefficient OPPs |
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On Wed, May 26, 2021 at 03:08:07PM +0530, Viresh Kumar wrote: > On 26-05-21, 10:01, Vincent Donnefort wrote: > > I originally considered to add the inefficient knowledge into the CPUFreq table. > > I wasn't talking about the cpufreq table here in the beginning, but calling > dev_pm_opp_disable(), which will eventually reflect in cpufreq table as well. > > > But I then gave up the idea for two reasons: > > > > * The EM depends on having schedutil enabled. I don't think that any > > other governor would then manage to rely on the inefficient OPPs. (also I > > believe Peter had a plan to keep schedutil as the one and only governor) > > Right, that EM is only there for schedutil. > > I would encourage if this can be done even without the EM dependency, if > possible. It would be a good thing to do generally for any driver that wants to > do that. > > > * The CPUfreq driver doesn't have to rely on the CPUfreq table, if the > > knowledge about inefficient OPPs is into the latter, some drivers might not > > be able to rely on the feature (you might say 'their loss' though :)) > > > > For those reasons, I thought that adding inefficient support into the > > CPUfreq table would complexify a lot the patchset for no functional gain. > > What about disabling the OPP in the OPP core itself ? So every user will get the > same picture. > > > > > > > Since the whole thing depends on EM and OPPs, I think we can actually do this. > > > > > > When the cpufreq driver registers with the EM core, lets find all the > > > Inefficient OPPs and disable them once and for all. Of course, this must be done > > > on voluntarily basis, a flag from the drivers will do. With this, we won't be > > > required to update any thing at any of the governors end. > > > > We still need to keep the inefficient OPPs for thermal reason. > > How will that benefit us if that OPP is never going to run anyway ? We won't be > cooling down the CPU then, isn't it ?
It would give more freedom for the cooling framework to pick a lower frequency to mitigate the current temperature even if we know this isn't, energy efficient.
As an example, on the Pixel4's SD855, the first 6 OPPs are inefficients on one of the cluster. If we hide those from the cooling framework, we'll prevent cooling for a quite wide range of frequencies.
That'd be however much more intrusive to support into cpufreq than just preventing the OPPs to be registered.
> > > But if we go with > > the inefficiency support into the CPUfreq table, we could enable or disable > > them, depending on the thermal pressure. Or add a flag to read the table with or > > without inefficient OPPs? > > Yeah, I was looking for a cpufreq driver flag or something like that so OPPs > don't disappear magically for some platforms which don't want it to happen. > > Moreover, a cpufreq driver first creates the OPP table, then registers with EM > or thermal. If we can play with that sequence a bit and make sure inefficient > OPPs are disabled before thermal or cpufreq tables are created, we will be good. > > -- > viresh
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