Messages in this thread | | | Subject | Re: [PATCH] sched/fair: Don't pull task if local group is more loaded than busiest group | From | "Li, Aubrey" <> | Date | Thu, 26 Mar 2020 09:51:47 +0800 |
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On 2020/3/25 21:43, Phil Auld wrote: > Hi Aubrey, > > On Wed, Mar 25, 2020 at 08:46:28PM +0800 Aubrey Li wrote: >> A huge number of load imbalance was observed when the local group >> type is group_fully_busy, and the average load of local group is >> greater than the selected busiest group, so the imbalance calculation >> returns a negative value actually. Fix this problem by comparing the >> average load before local group type check. >> >> Signed-off-by: Aubrey Li <aubrey.li@linux.intel.com> >> --- >> kernel/sched/fair.c | 14 +++++++------- >> 1 file changed, 7 insertions(+), 7 deletions(-) >> >> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c >> index c1217bf..c524369 100644 >> --- a/kernel/sched/fair.c >> +++ b/kernel/sched/fair.c >> @@ -8862,17 +8862,17 @@ static struct sched_group *find_busiest_group(struct lb_env *env) >> goto out_balanced; >> >> /* >> + * If the local group is more loaded than the selected >> + * busiest group don't try to pull any tasks. >> + */ >> + if (local->avg_load >= busiest->avg_load) >> + goto out_balanced; >> + >> + /* >> * When groups are overloaded, use the avg_load to ensure fairness >> * between tasks. >> */ >> if (local->group_type == group_overloaded) { >> - /* >> - * If the local group is more loaded than the selected >> - * busiest group don't try to pull any tasks. >> - */ >> - if (local->avg_load >= busiest->avg_load) >> - goto out_balanced; >> - >> /* XXX broken for overlapping NUMA groups */ >> sds.avg_load = (sds.total_load * SCHED_CAPACITY_SCALE) / >> sds.total_capacity; >> -- >> 2.7.4 >> > > I'm not sure about this. I think this patch will undo a good bit of the > benefit of the load balancer rework. Avg_load is really most useful > when things are overloaded. If we go back to looking at it here we may > fail to balance when needed. > > There are cases where, due to group scheduler load scaling, local average > may be higher but have spare CPUs still whereas busiest may have extra > processes which be balanced. > In my case, local group is fully busy, and the selected busiest group is overloaded, should we compute avg_idle for group_fully_busy as well?
Thanks, -Aubrey
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