On Thu, 2012-09-27 at 12:40 -0700, Linus Torvalds wrote: > I wonder about this comment, for example: > > * By using 'se' instead of 'curr' we penalize light tasks, so > * they get preempted easier. That is, if 'se' < 'curr' then > * the resulting gran will be larger, therefore penalizing the > * lighter, if otoh 'se' > 'curr' then the resulting gran will > * be smaller, again penalizing the lighter task. > > why would we want to preempt light tasks easier? It sounds backwards > to me. If they are light, we have *less* reason to preempt them, since > they are more likely to just go to sleep on their own, no?
No, weight is nice, you nicing a task doesn't make it want to run less. So preempting them sooner means they disturb the heavier less, which is I think what you want with nice. > Another question is whether the fact that this same load interacts > with select_idle_sibling() is perhaps a sign that maybe the preemption > logic is all fine, but it interacts badly with the "pick new cpu" > code. In particular, after having changed rq's, is the vruntime really > comparable? IOW, maybe this is an interaction between "place_entity()" > and then the immediately following (?) call to check wakeup > preemption? No, the vruntime comparison between cpus is dubious, its not complete nonsense but its not 'correct' either. PJT has patches to improve that based on his per-entity tracking stuff. -- 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/
