So maybe you want something like the below; that cures the thing Morten
raised, and we continue looking for sd, even after we found affine_sd.
It also avoids the pointless idle_cpu() check Mike raised by making
select_idle_sibling() return -1 if it doesn't find anything.
Then it continues doing the full balance IFF sd was set, which is keyed
off of sd->flags.
And note (as Mike already said), BALANCE_WAKE does _NOT_ look for idle
CPUs, it looks for the least loaded CPU. And its damn expensive.
Rewriting this entire thing is somewhere on the todo list :/
---
kernel/sched/fair.c | 36 +++++++++++++++++++++++-------------
1 file changed, 23 insertions(+), 13 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index d597aea43030..7330fb4fea9c 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1385,8 +1385,13 @@ static void task_numa_compare(struct task_numa_env *env,
* One idle CPU per node is evaluated for a task numa move.
* Call select_idle_sibling to maybe find a better one.
*/
- if (!cur)
- env->dst_cpu = select_idle_sibling(env->p, env->dst_cpu);
+ if (!cur) {
+ int cpu = select_idle_sibling(env->p, env->dst_cpu);
+ if (cpu < 0)
+ cpu = env->dst_cpu;
+
+ env->dst_cpu = cpu;
+ }
assign:
task_numa_assign(env, cur, imp);
@@ -4951,16 +4956,15 @@ static int select_idle_sibling(struct task_struct *p,
int target)
goto next;
}
- target = cpumask_first_and(sched_group_cpus(sg),
+ return cpumask_first_and(sched_group_cpus(sg),
tsk_cpus_allowed(p));
- goto done;
next:
sg = sg->next;
} while (sg != sd->groups);
}
-done:
- return target;
+ return -1;
}
+
/*
* get_cpu_usage returns the amount of capacity of a CPU that is used by CFS
* tasks. The unit of the return value must be the one of capacity so we can
@@ -5022,22 +5026,28 @@ select_task_rq_fair(struct task_struct *p, int
prev_cpu, int sd_flag, int wake_f
* If both cpu and prev_cpu are part of this domain,
* cpu is a valid SD_WAKE_AFFINE target.
*/
- if (want_affine && (tmp->flags & SD_WAKE_AFFINE) &&
- cpumask_test_cpu(prev_cpu, sched_domain_span(tmp))) {
+ if (want_affine && !affine_sd &&
+ (tmp->flags & SD_WAKE_AFFINE) &&
+ cpumask_test_cpu(prev_cpu, sched_domain_span(tmp)))
affine_sd = tmp;
- break;
- }
if (tmp->flags & sd_flag)
sd = tmp;
+ else if (!want_affine || (want_affine && affine_sd))
+ break;
}
- if (affine_sd && cpu != prev_cpu && wake_affine(affine_sd, p, sync))
+ if (affine_sd && cpu != prev_cpu && wake_affine(affine_sd, p, sync)) {
prev_cpu = cpu;
+ sd = NULL; /* WAKE_AFFINE trumps BALANCE_WAKE */
+ }
if (sd_flag & SD_BALANCE_WAKE) {
- new_cpu = select_idle_sibling(p, prev_cpu);
- goto unlock;
+ int tmp = select_idle_sibling(p, prev_cpu);
+ if (tmp >= 0) {
+ new_cpu = tmp;
+ goto unlock;
+ }
}
while (sd) {
--
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