Hi Viresh and Vincent, > On 9 April 2013 16:07, Lukasz Majewski <l.majewski@xxxxxxxxxxx> wrote: > >> On Mon, Apr 1, 2013 at 1:54 PM, Jonghwa Lee > > Our approach is a bit different than cpufreq_ondemand one. Ondemand > > takes the per CPU idle time, then on that basis calculates per cpu > > load. The next step is to choose the highest load and then use this > > value to properly scale frequency. > > > > On the other hand LAB tries to model different behavior: > > > > As a first step we applied Vincent Guittot's "pack small tasks" [*] > > patch to improve "race to idle" behavior: > > http://article.gmane.org/gmane.linux.kernel/1371435/match=sched+pack+small+tasks > > Luckily he is part of my team :) > > http://www.linaro.org/linux-on-arm/meet-the-team/power-management > > BTW, he is using ondemand governor for all his work. > > > Afterwards, we decided to investigate different approach for power > > governing: > > > > Use the number of sleeping CPUs (not the maximal per-CPU load) to > > change frequency. We thereof depend on [*] to "pack" as many tasks > > to CPU as possible and allow other to sleep. > > He packs only small tasks. What's about packing not only small tasks? I will investigate the possibility to aggressively pack (even with a cost of performance degradation) as many tasks as possible to a single CPU. It seems a good idea for a power consumption reduction. > And if there are many small tasks we are > packing, then load must be high and so ondemand gov will increase > freq. This is of course true for "packing" all tasks to a single CPU. If we stay at the power consumption envelope, we can even overclock the frequency. But what if other - lets say 3 CPUs - are under heavy workload? Ondemand will switch frequency to maximum, and as Jonghwa pointed out this can cause dangerous temperature increase. > > > Contrary, when all cores are heavily loaded, we decided to reduce > > frequency by around 30%. With this approach user experience > > recution is still acceptable (with much less power consumption). > > Don't know.. running many cpus at lower freq for long duration will > probably take more power than running them at high freq for short > duration and making system idle again. > > > We have posted this "RFC" patch mainly for discussion, and I think > > it fits its purpose :-). > > Yes, no issues with your RFC idea.. its perfect.. > > @Vincent: Can you please follow this thread a bit and tell us what > your views are? > > -- > viresh -- Best regards, Lukasz Majewski Samsung R&D Poland (SRPOL) | Linux Platform Group -- To unsubscribe from this list: send the line "unsubscribe cpufreq" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
