From e63da03639cc9e6e83b62e7ef8ffdbb92421416a Mon Sep 17 00:00:00 2001 From: Rik van Riel Date: Wed, 14 May 2014 13:22:21 -0400 Subject: [PATCH] sched/numa: Allow task switch if load imbalance improves Currently the NUMA balancing code only allows moving tasks between NUMA nodes when the load on both nodes is in balance. This breaks down when the load was imbalanced to begin with. Allow tasks to be moved between NUMA nodes if the imbalance is small, or if the new imbalance is be smaller than the original one. Suggested-by: Peter Zijlstra Signed-off-by: Rik van Riel Signed-off-by: Peter Zijlstra Cc: mgorman@suse.de Cc: chegu_vinod@hp.com Signed-off-by: Ingo Molnar Link: http://lkml.kernel.org/r/20140514132221.274b3463@annuminas.surriel.com --- kernel/sched/fair.c | 46 +++++++++++++++++++++++++++++++++++---------- 1 file changed, 36 insertions(+), 10 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index f7cac2ba62ea..b899613f2bc6 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -1095,6 +1095,34 @@ static void task_numa_assign(struct task_numa_env *env, env->best_cpu = env->dst_cpu; } +static bool load_too_imbalanced(long orig_src_load, long orig_dst_load, + long src_load, long dst_load, + struct task_numa_env *env) +{ + long imb, old_imb; + + /* We care about the slope of the imbalance, not the direction. */ + if (dst_load < src_load) + swap(dst_load, src_load); + + /* Is the difference below the threshold? */ + imb = dst_load * 100 - src_load * env->imbalance_pct; + if (imb <= 0) + return false; + + /* + * The imbalance is above the allowed threshold. + * Compare it with the old imbalance. + */ + if (orig_dst_load < orig_src_load) + swap(orig_dst_load, orig_src_load); + + old_imb = orig_dst_load * 100 - orig_src_load * env->imbalance_pct; + + /* Would this change make things worse? */ + return (old_imb > imb); +} + /* * This checks if the overall compute and NUMA accesses of the system would * be improved if the source tasks was migrated to the target dst_cpu taking @@ -1107,7 +1135,8 @@ static void task_numa_compare(struct task_numa_env *env, struct rq *src_rq = cpu_rq(env->src_cpu); struct rq *dst_rq = cpu_rq(env->dst_cpu); struct task_struct *cur; - long dst_load, src_load; + long orig_src_load, src_load; + long orig_dst_load, dst_load; long load; long imp = (groupimp > 0) ? groupimp : taskimp; @@ -1181,13 +1210,13 @@ static void task_numa_compare(struct task_numa_env *env, * In the overloaded case, try and keep the load balanced. */ balance: - dst_load = env->dst_stats.load; - src_load = env->src_stats.load; + orig_dst_load = env->dst_stats.load; + orig_src_load = env->src_stats.load; /* XXX missing power terms */ load = task_h_load(env->p); - dst_load += load; - src_load -= load; + dst_load = orig_dst_load + load; + src_load = orig_src_load - load; if (cur) { load = task_h_load(cur); @@ -1195,11 +1224,8 @@ balance: src_load += load; } - /* make src_load the smaller */ - if (dst_load < src_load) - swap(dst_load, src_load); - - if (src_load * env->imbalance_pct < dst_load * 100) + if (load_too_imbalanced(orig_src_load, orig_dst_load, + src_load, dst_load, env)) goto unlock; assign: -- 2.20.1