On 21 March 2016 at 11:53, Juri Lelli <juri.lelli@xxxxxxx> wrote: > Hi Sai, > > On 18/03/16 10:49, Sai Gurrappadi wrote: >> Hi Juri, >> >> On 03/18/2016 07:24 AM, Juri Lelli wrote: >> >> <snip> >> >> > + >> > +========================================== >> > +2 - CPU capacity definition >> > +========================================== >> > + >> > +CPU capacity is a number that provides the scheduler information about CPUs >> > +heterogeneity. Such heterogeneity can come from micro-architectural differences >> > +(e.g., ARM big.LITTLE systems) or maximum frequency at which CPUs can run >> > +(e.g., SMP systems with multiple frequency domains). Heterogeneity in this >> > +context is about differing performance characteristics; this binding tries to >> > +capture a first-order approximation of the relative performance of CPUs. >> >> Any reason why this capacity number is not dynamically generated based on the >> max frequency for each CPU? The DT property would then instead specify just >> the micro-architectural differences between the CPU types. >> > > I'm not sure I clearly understand your question, so I'll try to > reiterate it. > > Are you asking why we don't dynamically profile the system, at boot for > example, to get this number? Or do you ask why this number couldn't be > only describing micro-arch differences (so, if I get it right, we should > then multiply it by max freq to get the capacity of a CPU)? > > We already played with the first option (please refer to v2 and v3), but > we ended up agreeing that dynamic profiling adds overhead to the boot > process (while a DT approach can provide information to speed up boot) > and it is in general not repeatable/reliable (as numbers can vary from > boot to boot for different reasons). > > The second option I think can be feasible, but I'm not sure what we gain > in practice. We will still need to specify a per-platform number, right? So could we use dt binding like dhrystone = <xyz> (with a unit like DMIPS/Mhz) which can then be combined with OPP table to gives a 1st-order approximation of each CPU capacity ? > > Best, > > - Juri -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
