On Friday, March 28, 2014 01:29:53 PM Daniel Lezcano wrote: > The following patchset provides an interaction between cpuidle and the > scheduler. > > The first patch encapsulate the needed information for the scheduler in a > separate cpuidle structure. The second one stores the pointer to this > structure > when entering idle. The third one, use this information to take the decision > to > find the idlest cpu. > > After some basic testing with hackbench, it appears there is an improvement > for > the performances (small) and for the duration of the idle states (which > provides > a better power saving). > > The measurement has been done with the 'idlestat' tool previously posted in > this > mailing list. > > So the benefit is good for both sides performance and power saving. > > The select_idle_sibling could be also improved in the same way.
Well, quite frankly, I don't really like this series. Not the idea itself, but the way it has been implemented. First off, if the scheduler is to access idle state data stored in struct cpuidle_state, I'm not sure why we need a separate new structure for that? Couldn't there be a pointer to a whole struct cpuidle_state from struct rq instead? [->exit_latency is the only field that find_idlest_cpu() in your third patch seems to be using anyway.] Second, is accessing the idle state information for all CPUs from find_idlest_cpu() guaranteed to be non-racy? I mean, what if a CPU changes its state from idle to non-idle while another one is executing find_idlest_cpu()? In other words, where's the read memory barrier corresponding to the write ones in the modified cpu_idle_call()? And is the memory barrier actually sufficient? After all, you need to guarantee that the CPU is still idle after you have evaluated idle_cpu() on it. Finally, is really the heuristics used by find_idlest_cpu() to select the "idlest" CPU the best one? What about deeper vs shallower idle states, for example? Rafael -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
