On Tue, Apr 06, 2021 at 04:17:10PM -0700, Ricardo Neri wrote: > On Tue, Apr 06, 2021 at 01:17:28PM +0200, Peter Zijlstra wrote: > > On Mon, Apr 05, 2021 at 09:11:07PM -0700, Ricardo Neri wrote: > > > @@ -8507,6 +8619,10 @@ static bool update_sd_pick_busiest(struct lb_env > > > *env, > > > if (!sgs->sum_h_nr_running) > > > return false; > > > > > > + if (sgs->group_type == group_asym_packing && > > > + !asym_can_pull_tasks(env->dst_cpu, sds, sgs, sg)) > > > + return false; > > > > All of this makes my head hurt; but afaict this isn't right. > > > > Your update_sg_lb_stats() change makes that we unconditionally set > > sgs->group_asym_packing, and then this is to undo that. But it's not > > clear this covers all cases right. > > We could not make a decision to set sgs->group_asym_packing in > update_sg_lb_stats() because we don't have information about the dst_cpu > and its SMT siblings if any. That is the reason I proposed to delay the > decision to update_sd_pick_busiest(), where we can compare local and > sgs.
Yeah, I sorta got that. > > Even if !sched_asym_prefer(), we could end up selecting this sg as > > busiest, but you're just bailing out here. > > Even if sgs->group_asym_packing is unconditionally set, sgs can still > be classified as group_overloaded and group_imbalanced. In such cases > we wouldn't bailout. sgs could not be classified as group_fully_busy > or group_has_spare and we would bailout, though. Is your concern about > these? I can fixup these two cases. Yes. Either explain (in a comment) why those cases are not relevant, or handle them properly. Because when reading this, it wasn't at all obvious that this is correct or as intended.
