sched/numa: Remove numa_has_capacity()

task_numa_find_cpu() helps to find the CPU to swap/move the task to.
It's guarded by numa_has_capacity(). However node not having capacity
shouldn't deter a task swapping if it helps NUMA placement.

Further load_too_imbalanced(), which evaluates possibilities of move/swap,
provides similar checks as numa_has_capacity.

Hence remove numa_has_capacity() to enhance possibilities of task
swapping even if load is imbalanced.

Running SPECjbb2005 on a 4 node machine and comparing bops/JVM
JVMS  LAST_PATCH  WITH_PATCH  %CHANGE
16    25657.9     25804.1     0.569
1     74435       73413       -1.37

Signed-off-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Rik van Riel <riel@surriel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1529514181-9842-13-git-send-email-srikar@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 7b4eddec3ccc89f265df0ae415cf395acefadd99..3bcf0e864613d079eb75c34176724e06d82898d1 100644 (file)
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1456,7 +1456,6 @@ struct numa_stats {
        unsigned long compute_capacity;
 
        unsigned int nr_running;
-       int has_free_capacity;
 };
 
 /*
@@ -1483,8 +1482,7 @@ static void update_numa_stats(struct numa_stats *ns, int nid)
         * the @ns structure is NULL'ed and task_numa_compare() will
         * not find this node attractive.
         *
-        * We'll either bail at !has_free_capacity, or we'll detect a huge
-        * imbalance and bail there.
+        * We'll detect a huge imbalance and bail there.
         */
        if (!cpus)
                return;
@@ -1495,7 +1493,6 @@ static void update_numa_stats(struct numa_stats *ns, int nid)
 
        capacity = min_t(unsigned, capacity,
                DIV_ROUND_CLOSEST(ns->compute_capacity, SCHED_CAPACITY_SCALE));
-       ns->has_free_capacity = (ns->nr_running < capacity);
 }
 
 struct task_numa_env {
@@ -1698,31 +1695,6 @@ static void task_numa_find_cpu(struct task_numa_env *env,
        }
 }
 
-/* Only move tasks to a NUMA node less busy than the current node. */
-static bool numa_has_capacity(struct task_numa_env *env)
-{
-       struct numa_stats *src = &env->src_stats;
-       struct numa_stats *dst = &env->dst_stats;
-
-       if (src->has_free_capacity && !dst->has_free_capacity)
-               return false;
-
-       /*
-        * Only consider a task move if the source has a higher load
-        * than the destination, corrected for CPU capacity on each node.
-        *
-        *      src->load                dst->load
-        * --------------------- vs ---------------------
-        * src->compute_capacity    dst->compute_capacity
-        */
-       if (src->load * dst->compute_capacity * env->imbalance_pct >
-
-           dst->load * src->compute_capacity * 100)
-               return true;
-
-       return false;
-}
-
 static int task_numa_migrate(struct task_struct *p)
 {
        struct task_numa_env env = {
@@ -1777,8 +1749,7 @@ static int task_numa_migrate(struct task_struct *p)
        update_numa_stats(&env.dst_stats, env.dst_nid);
 
        /* Try to find a spot on the preferred nid. */
-       if (numa_has_capacity(&env))
-               task_numa_find_cpu(&env, taskimp, groupimp);
+       task_numa_find_cpu(&env, taskimp, groupimp);
 
        /*
         * Look at other nodes in these cases:
@@ -1808,8 +1779,7 @@ static int task_numa_migrate(struct task_struct *p)
                        env.dist = dist;
                        env.dst_nid = nid;
                        update_numa_stats(&env.dst_stats, env.dst_nid);
-                       if (numa_has_capacity(&env))
-                               task_numa_find_cpu(&env, taskimp, groupimp);
+                       task_numa_find_cpu(&env, taskimp, groupimp);
                }
        }