Messages in this thread Patch in this message | | | From | Vincent Guittot <> | Subject | [PATCH] sched/fair: ensure tasks spreading in LLC during LB | Date | Mon, 2 Nov 2020 11:24:57 +0100 |
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schbench shows latency increase for 95 percentile above since: commit 0b0695f2b34a ("sched/fair: Rework load_balance()")
Align the behavior of the load balancer with the wake up path, which tries to select an idle CPU which belongs to the LLC for a waking task.
calculate_imbalance() will use nr_running instead of the spare capacity when CPUs share resources (ie cache) at the domain level. This will ensure a better spread of tasks on idle CPUs.
Running schbench on a hikey (8cores arm64) shows the problem:
tip/sched/core : schbench -m 2 -t 4 -s 10000 -c 1000000 -r 10 Latency percentiles (usec) 50.0th: 33 75.0th: 45 90.0th: 51 95.0th: 4152 *99.0th: 14288 99.5th: 14288 99.9th: 14288 min=0, max=14276
tip/sched/core + patch : schbench -m 2 -t 4 -s 10000 -c 1000000 -r 10 Latency percentiles (usec) 50.0th: 34 75.0th: 47 90.0th: 52 95.0th: 78 *99.0th: 94 99.5th: 94 99.9th: 94 min=0, max=94
Fixes: 0b0695f2b34a ("sched/fair: Rework load_balance()") Reported-by: Chris Mason <clm@fb.com> Suggested-by: Rik van Riel <riel@surriel.com> Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org> --- kernel/sched/fair.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index aa4c6227cd6d..210b15f068a6 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -9031,7 +9031,8 @@ static inline void calculate_imbalance(struct lb_env *env, struct sd_lb_stats *s * emptying busiest. */ if (local->group_type == group_has_spare) { - if (busiest->group_type > group_fully_busy) { + if ((busiest->group_type > group_fully_busy) && + !(env->sd->flags & SD_SHARE_PKG_RESOURCES)) { /* * If busiest is overloaded, try to fill spare * capacity. This might end up creating spare capacity -- 2.17.1
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