Messages in this thread | | | From | Vincent Guittot <> | Date | Wed, 30 Jul 2014 11:32:36 +0200 | Subject | Re: [PATCH 1/2] sched: fix and clean up calculate_imbalance |
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On 29 July 2014 17:27, Peter Zijlstra <peterz@infradead.org> wrote: > 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
FWIW, you can add my ack for the new version of the patchset which includes this patch
> > --- > Subject: sched,fair: Allow calculate_imbalance() to move idle cpus > From: Peter Zijlstra <peterz@infradead.org> > 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 <riel@redhat.com> > Signed-off-by: Peter Zijlstra <peterz@infradead.org> > Link: http://lkml.kernel.org/n/tip-7k95k4i2tjv78iivstggiude@git.kernel.org > --- > 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); >
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