On 02/09/2016 02:37 AM, Juri Lelli wrote: >> I'm still concerned that there's no way to obtain optimal boot time on a >> > heterogeneous system. Either the dynamic benchmarking is enabled, adding >> > 1 sec, or the benchmarking is skipped, and task distribution on the >> > heterogeneous CPUs is determined by the platform's CPU numbering and >> > chance, potentially impacting performance nondeterministically until >> > userspace sets the correct capacity values via sysfs. >> > >> > I believe you tested the impact on boot time of using equal capacity >> > values and saw little difference. I'm wondering though, what was the CPU >> > numbering on that target? >> > > > My targets (Juno and TC2) had big cluster on 1,2 and little on the > remaining cpus. Why do you think this might matter? There's a natural bias in the scheduler AFAIK towards lower-numbered CPUs since they are typically scanned in numerically ascending order. So when all capacities are initially defaulted to be the same I think you'll be more likely to use the lower numbered CPUs. I'd be curious what the performance penalty is on a b.L system where the lowest numbered CPUs are small. I don't have such a target but maybe it's possible to compare booting just with bigs vs just with littles, at least until userspace intializes and a script can bring up the others, which is the same point at which capacities could be properly set. That would give something of an upper bound. > Anyway, IMHO boot time performance is not what we are targeting here, so > I wouldn't be too worried about this particular point. It may not be the most important thing but it is a factor worth considering - as mentioned earlier there are applications where boot time is critical such as automotive. It seems unfortunate that actual performance may be left on the table due to (IMO anyway) a tenuous concern over DT semantics. But it looks like that may just be my position :/ . thanks, Steve -- 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
