On Tue, Jul 29, 2014 at 04:59:10PM +0200, Peter Zijlstra wrote: > On Tue, Jul 29, 2014 at 11:04:50AM +0200, Vincent Guittot wrote: > > > In situations where all the domains are overloaded, or where only the > > > busiest domain is overloaded, that code is also superfluous, since > > > the normal env->imbalance calculation will figure out how much to move. > > > Remove the load_above_capacity calculation. > > > > IMHO, we should not remove that part which is used by prefer_sibling > > > > Originally, we had 2 type of busiest group: overloaded or imbalanced. > > You add a new one which has only a avg_load higher than other so you > > should handle this new case and keep the other ones unchanged > > Right, so we want that code for overloaded -> overloaded migrations such > as not to cause idle cpus in an attempt to balance things. Idle cpus are > worse than imbalance. > > But in case of overloaded/imb -> !overloaded migrations we can allow it, > and in fact want to allow it in order to balance idle cpus.
Which would be patch 3/2 --- Subject: sched,fair: Allow calculate_imbalance() to move idle cpus From: Peter Zijlstra <[email protected]> Date: Tue Jul 29 17:15:11 CEST 2014 Allow calculate_imbalance() to 'create' idle cpus in the busiest group if there are idle cpus in the local group. Suggested-by: Rik van Riel <[email protected]> Signed-off-by: Peter Zijlstra <[email protected]> Link: http://lkml.kernel.org/n/[email protected] --- kernel/sched/fair.c | 11 +++++------ 1 file changed, 5 insertions(+), 6 deletions(-) --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -6273,12 +6273,11 @@ static inline void calculate_imbalance(s return fix_small_imbalance(env, sds); } - if (busiest->group_type == group_overloaded) { - /* - * Don't want to pull so many tasks that a group would go idle. - * Except of course for the group_imb case, since then we might - * have to drop below capacity to reach cpu-load equilibrium. - */ + /* + * If there aren't any idle cpus, avoid creating some. + */ + if (busiest->group_type == group_overloaded && + local->group_type == group_overloaded) { load_above_capacity = (busiest->sum_nr_running - busiest->group_capacity_factor); -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
