Messages in this thread | | | Subject | Re: [PATCH v2 0/3] EM / PM: Inefficient OPPs | From | Lukasz Luba <> | Date | Wed, 26 May 2021 11:39:27 +0100 |
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On 5/26/21 11:24 AM, Lukasz Luba wrote:
[snip]
>> What about disabling the OPP in the OPP core itself ? So every user >> will get the >> same picture. > > There are SoCs which have OPPs every 100MHz even at high freq. They are > used e.g. when thermal kicks in. We shouldn't disable them in generic > frameworks like OPP. They might be used to provide enough CPU capacity, > when temp is high. Imagine you have a board which does some work: > sends and received some UDP packets. The board has been tested in oven > that it will still be able to handle X messages/sec but using an OPP, > which in our heuristic is 'inefficient'. You cannot go above, because it > will overheat the SoC, you might go below and find first 'efficient' > OPP. You might harm this board performance if e.g. the OPP is 20% slower > that this 'inefficient' which was tested by engineers. > >> >>>> >>>> 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 > > This OPP still might be used, the Vincent heuristic is just a 'hint'. > Schedutil will check policy->max and could clamp the 'efficient' > returned freq to first allowed, which might be 'inefficient' > >> cooling down the CPU then, isn't it ? > > The 'inefficient' OPP is called from our 'energy placement' angle. For > other folks from automotive, industrial or IoT who are stress testing > SoCs and boards in various circumstances, they might call our > 'inefficient' perf state as 'efficient' - for they need. > > In our internal review I pointed that we are optimizing for mobiles with > this and we might actually need a #ifdef, config or a switch for this > heuristic. >
But even in mobiles, we might start facing issues e.g. during high resolution recording, when we just disable 'inefficient' OPPs, which were used in such use case and higher temperature.
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