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Commit16b0a7a

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vingu-linaroPeter Zijlstra
authored and
Peter Zijlstra
committed
sched/fair: Ensure tasks spreading in LLC during LB
schbench shows latency increase for 95 percentile above since: commit0b0695f ("sched/fair: Rework load_balance()")Align the behavior of the load balancer with the wake up path, which triesto select an idle CPU which belongs to the LLC for a waking task.calculate_imbalance() will use nr_running instead of the sparecapacity when CPUs share resources (ie cache) at the domain level. Thiswill 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 -c1000000 -r 10Latency percentiles (usec)50.0th: 3375.0th: 4590.0th: 5195.0th: 4152*99.0th: 1428899.5th: 1428899.9th: 14288min=0, max=14276tip/sched/core + patch :schbench -m 2 -t 4 -s 10000 -c1000000 -r 10Latency percentiles (usec)50.0th: 3475.0th: 4790.0th: 5295.0th: 78*99.0th: 9499.5th: 9499.9th: 94min=0, max=94Fixes:0b0695f ("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>Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>Reviewed-by: Rik van Riel <riel@surriel.com>Tested-by: Rik van Riel <riel@surriel.com>Link:https://lkml.kernel.org/r/20201102102457.28808-1-vincent.guittot@linaro.org
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‎kernel/sched/fair.c‎

Lines changed: 2 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -9031,7 +9031,8 @@ static inline void calculate_imbalance(struct lb_env *env, struct sd_lb_stats *s
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* emptying busiest.
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*/
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if (local->group_type==group_has_spare) {
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if (busiest->group_type>group_fully_busy) {
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if ((busiest->group_type>group_fully_busy)&&
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!(env->sd->flags&SD_SHARE_PKG_RESOURCES)) {
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/*
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* If busiest is overloaded, try to fill spare
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* capacity. This might end up creating spare capacity

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