linux-kernel - Re: [PATCH V3 0/2] load_balance() fixes for affinity

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Date:   Mon, 22 May 2017 17:52:17 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Jeffrey Hugo <jhugo@...eaurora.org>
Cc:     Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Austin Christ <austinwc@...eaurora.org>,
        Tyler Baicar <tbaicar@...eaurora.org>,
        Timur Tabi <timur@...eaurora.org>
Subject: Re: [PATCH V3 0/2] load_balance() fixes for affinity

On Thu, May 18, 2017 at 01:36:01PM -0600, Jeffrey Hugo wrote:

> The group_imbalance path correctly sets the flag
> to indicate the group can not be properly balanced due to affinity, but the
> redo condition right after this branch incorrectly assumes that there may
> be other cores with work to be pulled by considering cores outside of the
> scheduling domain in question.

So its been a while since I looked at any of this, but from a quick
look, env->cpus appears to only be applied to group/balance masks.

In which case, we can easily do something like the below. Did I miss
something?

---
 kernel/sched/fair.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 219fe58e3023..1724e4433f89 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -8104,7 +8104,7 @@ static int load_balance(int this_cpu, struct rq *this_rq,
 	if (idle == CPU_NEWLY_IDLE)
 		env.dst_grpmask = NULL;
 
-	cpumask_copy(cpus, cpu_active_mask);
+	cpumask_and(cpus, sched_domain_span(sd), cpu_active_mask);
 
 	schedstat_inc(sd->lb_count[idle]);