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sched/numa: Stop an exhastive search if a reasonable swap candidate or idle CPU is found

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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
This commit is contained in:
Mel Gorman 2020-02-24 09:52:23 +00:00 committed by Ingo Molnar
parent 88cca72c96
commit a0f03b617c
1 changed files with 27 additions and 4 deletions
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31
kernel/sched/fair.c
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@ -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;
}
}