On Thu, May 29, 2014 at 09:37:39PM +0200, Vincent Guittot wrote: > On 29 May 2014 11:50, Peter Zijlstra <pet...@infradead.org> wrote: > > On Fri, May 23, 2014 at 05:53:04PM +0200, Vincent Guittot wrote: > >> If the CPU is used for handling lot of IRQs, trig a load balance to check > >> if > >> it's worth moving its tasks on another CPU that has more capacity > >> > >> Signed-off-by: Vincent Guittot <vincent.guit...@linaro.org> > >> --- > >> kernel/sched/fair.c | 13 +++++++++++++ > >> 1 file changed, 13 insertions(+) > >> > >> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > >> index e8a30f9..2501e49 100644 > >> --- a/kernel/sched/fair.c > >> +++ b/kernel/sched/fair.c > >> @@ -5948,6 +5948,13 @@ static bool update_sd_pick_busiest(struct lb_env > >> *env, > >> if (sgs->sum_nr_running > sgs->group_capacity) > >> return true; > >> > >> + /* > >> + * The group capacity is reduced probably because of activity from > >> other > >> + * sched class or interrupts which use part of the available capacity > >> + */ > >> + if ((sg->sgp->power_orig * 100) > (sgs->group_power * > >> env->sd->imbalance_pct)) > >> + return true; > >> + > >> if (sgs->group_imb) > >> return true; > >> > > > > But we should already do this because the load numbers are scaled with > > the power/capacity figures. If one CPU gets significant less time to run > > fair tasks, its effective load would spike and it'd get to be selected > > here anyway. > > > > Or am I missing something? > > The CPU could have been picked when the capacity becomes null (which > occurred when the cpu_power goes below half the default > SCHED_POWER_SCALE). And even after that, there were some conditions in > find_busiest_group that was bypassing this busiest group
Could you detail those conditions? FWIW those make excellent Changelog material.
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