From: Mel Gorman <mgorman@techsingularity.net>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>,
Vincent Guittot <vincent.guittot@linaro.org>,
Juri Lelli <juri.lelli@redhat.com>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Steven Rostedt <rostedt@goodmis.org>,
Ben Segall <bsegall@google.com>,
Valentin Schneider <valentin.schneider@arm.com>,
Phil Auld <pauld@redhat.com>, Hillf Danton <hdanton@sina.com>,
LKML <linux-kernel@vger.kernel.org>,
Mel Gorman <mgorman@techsingularity.net>
Subject: [PATCH 13/13] sched/numa: Stop an exhastive search if a reasonable swap candidate or idle CPU is found
Date: Wed, 19 Feb 2020 13:54:42 +0000 [thread overview]
Message-ID: <20200219135442.18107-14-mgorman@techsingularity.net> (raw)
In-Reply-To: <20200219135442.18107-1-mgorman@techsingularity.net>
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 935baf529f10..a1d5760f7985 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) {
+ stopsearch = 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
next prev parent reply other threads:[~2020-02-19 13:57 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-19 13:54 [PATCH 00/13] Reconcile NUMA balancing decisions with the load balancer v4 Mel Gorman
2020-02-19 13:54 ` [PATCH 01/13] sched/fair: Allow a per-CPU kthread waking a task to stack on the same CPU, to fix XFS performance regression Mel Gorman
2020-02-19 13:54 ` [PATCH 02/13] sched/numa: Trace when no candidate CPU was found on the preferred node Mel Gorman
2020-02-19 13:54 ` [PATCH 03/13] sched/numa: Distinguish between the different task_numa_migrate failure cases Mel Gorman
2020-02-19 13:54 ` [PATCH 04/13] sched/fair: Reorder enqueue/dequeue_task_fair path Mel Gorman
2020-02-19 13:54 ` [PATCH 05/13] sched/numa: Replace runnable_load_avg by load_avg Mel Gorman
2020-02-19 13:54 ` [PATCH 06/13] sched/numa: Use similar logic to the load balancer for moving between domains with spare capacity Mel Gorman
2020-02-19 13:54 ` [PATCH 07/13] sched/pelt: Remove unused runnable load average Mel Gorman
2020-02-19 13:54 ` [PATCH 08/13] sched/pelt: Add a new runnable average signal Mel Gorman
2020-02-19 13:54 ` [PATCH 09/13] sched/fair: Take into account runnable_avg to classify group Mel Gorman
2020-02-19 13:54 ` [PATCH 10/13] sched/numa: Prefer using an idle cpu as a migration target instead of comparing tasks Mel Gorman
2020-02-19 13:54 ` [PATCH 11/13] sched/numa: Find an alternative idle CPU if the CPU is part of an active NUMA balance Mel Gorman
2020-02-19 13:54 ` [PATCH 12/13] sched/numa: Bias swapping tasks based on their preferred node Mel Gorman
2020-02-19 13:54 ` Mel Gorman [this message]
2020-02-19 14:06 ` [PATCH 00/13] Reconcile NUMA balancing decisions with the load balancer v4 Mel Gorman
-- strict thread matches above, loose matches on Subject: below --
2020-02-24 9:52 [PATCH 00/13] Reconcile NUMA balancing decisions with the load balancer v6 Mel Gorman
2020-02-24 9:52 ` [PATCH 13/13] sched/numa: Stop an exhastive search if a reasonable swap candidate or idle CPU is found Mel Gorman
2020-02-19 14:07 [PATCH 00/13] Reconcile NUMA balancing decisions with the load balancer v5 Mel Gorman
2020-02-19 14:07 ` [PATCH 13/13] sched/numa: Stop an exhastive search if a reasonable swap candidate or idle CPU is found Mel Gorman
2020-02-17 10:43 [PATCH 00/13] Reconcile NUMA balancing decisions with the load balancer v3 Mel Gorman
2020-02-17 10:44 ` [PATCH 13/13] sched/numa: Stop an exhastive search if a reasonable swap candidate or idle CPU is found Mel Gorman
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