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

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Message-ID: <8716629f-6ccb-bfa1-62d5-3fee6b9f9316@codeaurora.org>
Date:   Mon, 22 May 2017 14:17:17 -0600
From:   "Christ, Austin" <austinwc@...eaurora.org>
To:     Peter Zijlstra <peterz@...radead.org>,
        Jeffrey Hugo <jhugo@...eaurora.org>
Cc:     Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Tyler Baicar <tbaicar@...eaurora.org>,
        Timur Tabi <timur@...eaurora.org>
Subject: Re: [PATCH V3 0/2] load_balance() fixes for affinity

Hey Peter,


On 5/22/2017 9:52 AM, Peter Zijlstra wrote:
> 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?
We have looked through and agree with your proposed change; however, we 
would still need to mask out the dst_cpu when considering the redo path. 
We will include this modification in the next patch set.
>
> ---
>   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]);
>   

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