| Message ID | 1571405198-27570-8-git-send-email-vincent.guittot@linaro.org |
|---|---|
| State | New |
| Headers | show |
| Series | sched/fair: rework the CFS load balance | expand |
On Fri, Oct 18, 2019 at 03:26:34PM +0200, Vincent Guittot wrote: > When there is only 1 cpu per group, using the idle cpus to evenly spread > tasks doesn't make sense and nr_running is a better metrics. > > Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org> > --- > kernel/sched/fair.c | 40 ++++++++++++++++++++++++++++------------ > 1 file changed, 28 insertions(+), 12 deletions(-) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 9ac2264..9b8e20d 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -8601,18 +8601,34 @@ static struct sched_group *find_busiest_group(struct lb_env *env) > busiest->sum_nr_running > local->sum_nr_running + 1) > goto force_balance; > > - if (busiest->group_type != group_overloaded && > - (env->idle == CPU_NOT_IDLE || > - local->idle_cpus <= (busiest->idle_cpus + 1))) > - /* > - * If the busiest group is not overloaded > - * and there is no imbalance between this and busiest group > - * wrt idle CPUs, it is balanced. The imbalance > - * becomes significant if the diff is greater than 1 otherwise > - * we might end up to just move the imbalance on another > - * group. > - */ > - goto out_balanced; > + if (busiest->group_type != group_overloaded) { > + if (env->idle == CPU_NOT_IDLE) > + /* > + * If the busiest group is not overloaded (and as a > + * result the local one too) but this cpu is already > + * busy, let another idle cpu try to pull task. > + */ > + goto out_balanced; > + > + if (busiest->group_weight > 1 && > + local->idle_cpus <= (busiest->idle_cpus + 1)) > + /* > + * If the busiest group is not overloaded > + * and there is no imbalance between this and busiest > + * group wrt idle CPUs, it is balanced. The imbalance > + * becomes significant if the diff is greater than 1 > + * otherwise we might end up to just move the imbalance > + * on another group. Of course this applies only if > + * there is more than 1 CPU per group. > + */ > + goto out_balanced; > + > + if (busiest->sum_h_nr_running == 1) > + /* > + * busiest doesn't have any tasks waiting to run > + */ > + goto out_balanced; > + } > While outside the scope of this patch, it appears that this would still allow slight imbalances in idle CPUs to pull tasks across NUMA domains too easily. -- Mel Gorman SUSE Labs
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 9ac2264..9b8e20d 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -8601,18 +8601,34 @@ static struct sched_group *find_busiest_group(struct lb_env *env) busiest->sum_nr_running > local->sum_nr_running + 1) goto force_balance; - if (busiest->group_type != group_overloaded && - (env->idle == CPU_NOT_IDLE || - local->idle_cpus <= (busiest->idle_cpus + 1))) - /* - * If the busiest group is not overloaded - * and there is no imbalance between this and busiest group - * wrt idle CPUs, it is balanced. The imbalance - * becomes significant if the diff is greater than 1 otherwise - * we might end up to just move the imbalance on another - * group. - */ - goto out_balanced; + if (busiest->group_type != group_overloaded) { + if (env->idle == CPU_NOT_IDLE) + /* + * If the busiest group is not overloaded (and as a + * result the local one too) but this cpu is already + * busy, let another idle cpu try to pull task. + */ + goto out_balanced; + + if (busiest->group_weight > 1 && + local->idle_cpus <= (busiest->idle_cpus + 1)) + /* + * If the busiest group is not overloaded + * and there is no imbalance between this and busiest + * group wrt idle CPUs, it is balanced. The imbalance + * becomes significant if the diff is greater than 1 + * otherwise we might end up to just move the imbalance + * on another group. Of course this applies only if + * there is more than 1 CPU per group. + */ + goto out_balanced; + + if (busiest->sum_h_nr_running == 1) + /* + * busiest doesn't have any tasks waiting to run + */ + goto out_balanced; + } force_balance: /* Looks like there is an imbalance. Compute it */
When there is only 1 cpu per group, using the idle cpus to evenly spread tasks doesn't make sense and nr_running is a better metrics. Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org> --- kernel/sched/fair.c | 40 ++++++++++++++++++++++++++++------------ 1 file changed, 28 insertions(+), 12 deletions(-) -- 2.7.4