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Subject[tip:sched/core] sched/numa: Remove numa_has_capacity()
Commit-ID:  2d4056fafa196e1ab4e7161bae4df76f9602d56d
Gitweb: https://git.kernel.org/tip/2d4056fafa196e1ab4e7161bae4df76f9602d56d
Author: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
AuthorDate: Wed, 20 Jun 2018 22:32:53 +0530
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Wed, 25 Jul 2018 11:41:08 +0200

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>
---
kernel/sched/fair.c | 36 +++---------------------------------
1 file changed, 3 insertions(+), 33 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 7b4eddec3ccc..3bcf0e864613 100644
--- 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);
}
}

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