lkml.org 
[lkml]   [2020]   [Feb]   [14]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
Subject[PATCH 12/12] sched/numa: Stop an exhastive search if a reasonable swap candidate or idle CPU is found
When domains are imbalanced or overloaded a search of all CPUs on the
target domain is searched and compared with task_numa_compare. In some
circumstances, a candidate is found that is an obvious win.

o A task can move to an idle CPU and an idle CPU is found
o A swap candidate is found that would move to its preferred domain

This patch terminates the search when either condition is met.

Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
---
kernel/sched/fair.c | 31 +++++++++++++++++++++++++++----
1 file changed, 27 insertions(+), 4 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index d046fa97b7ef..4870eed91857 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1707,7 +1707,7 @@ static bool load_too_imbalanced(long src_load, long dst_load,
* into account that it might be best if task running on the dst_cpu should
* be exchanged with the source task
*/
-static void task_numa_compare(struct task_numa_env *env,
+static bool task_numa_compare(struct task_numa_env *env,
long taskimp, long groupimp, bool maymove)
{
struct numa_group *cur_ng, *p_ng = deref_curr_numa_group(env->p);
@@ -1718,9 +1718,10 @@ static void task_numa_compare(struct task_numa_env *env,
int dist = env->dist;
long moveimp = imp;
long load;
+ bool stopsearch = false;

if (READ_ONCE(dst_rq->numa_migrate_on))
- return;
+ return false;

rcu_read_lock();
cur = rcu_dereference(dst_rq->curr);
@@ -1731,8 +1732,10 @@ static void task_numa_compare(struct task_numa_env *env,
* Because we have preemption enabled we can get migrated around and
* end try selecting ourselves (current == env->p) as a swap candidate.
*/
- if (cur == env->p)
+ if (cur == env->p) {
+ stopsearch = true;
goto unlock;
+ }

if (!cur) {
if (maymove && moveimp >= env->best_imp)
@@ -1860,8 +1863,27 @@ static void task_numa_compare(struct task_numa_env *env,
}

task_numa_assign(env, cur, imp);
+
+ /*
+ * If a move to idle is allowed because there is capacity or load
+ * balance improves then stop the search. While a better swap
+ * candidate may exist, a search is not free.
+ */
+ if (maymove && !cur && env->best_cpu >= 0 && idle_cpu(env->best_cpu))
+ stopsearch = true;
+
+ /*
+ * If a swap candidate must be identified and the current best task
+ * moves its preferred node then stop the search.
+ */
+ if (!maymove && env->best_task &&
+ env->best_task->numa_preferred_nid == env->src_nid) {
+ return true;
+ }
unlock:
rcu_read_unlock();
+
+ return stopsearch;
}

static void task_numa_find_cpu(struct task_numa_env *env,
@@ -1911,7 +1933,8 @@ static void task_numa_find_cpu(struct task_numa_env *env,
continue;

env->dst_cpu = cpu;
- task_numa_compare(env, taskimp, groupimp, maymove);
+ if (task_numa_compare(env, taskimp, groupimp, maymove))
+ break;
}
}

--
2.16.4
\
 
 \ /
  Last update: 2020-02-14 09:19    [W:0.057 / U:1.976 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site