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authorMel Gorman <mgorman@techsingularity.net>2020-02-24 09:52:23 +0000
committerIngo Molnar <mingo@kernel.org>2020-02-24 11:36:40 +0100
commita0f03b617c3b2644d3d47bf7d9e60aed01bd5b10 (patch)
tree4e2326bb2ff040ad2139c5fd0c6c3aa143c67a81 /kernel/sched/fair.c
parent88cca72c9673e631b63eca7a1dba4a9722a3f414 (diff)
downloadlinux-a0f03b617c3b2644d3d47bf7d9e60aed01bd5b10.tar.gz
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> Signed-off-by: Ingo Molnar <mingo@kernel.org> Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Vincent Guittot <vincent.guittot@linaro.org> Cc: Juri Lelli <juri.lelli@redhat.com> Cc: Dietmar Eggemann <dietmar.eggemann@arm.com> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Valentin Schneider <valentin.schneider@arm.com> Cc: Phil Auld <pauld@redhat.com> Cc: Hillf Danton <hdanton@sina.com> Link: https://lore.kernel.org/r/20200224095223.13361-14-mgorman@techsingularity.net
Diffstat (limited to 'kernel/sched/fair.c')
-rw-r--r--kernel/sched/fair.c31
1 files changed, 27 insertions, 4 deletions
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 8c1ac01a10d5..fcc968669aea 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 @@ assign:
}
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) {
+ stopsearch = true;
+ }
unlock:
rcu_read_unlock();
+
+ return stopsearch;
}
static void task_numa_find_cpu(struct task_numa_env *env,
@@ -1916,7 +1938,8 @@ 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;
}
}