linux-kernel - Re: [RESEND PATCH] sched/fair: consider RT/IRQ pressure in select_idle

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Message-ID: <14d6cf2f-b987-6987-0f9e-df03ba84d989@oracle.com>
Date:   Fri, 9 Feb 2018 14:05:17 -0800
From:   Rohit Jain <rohit.k.jain@...cle.com>
To:     Dietmar Eggemann <dietmar.eggemann@....com>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     mingo@...hat.com, linux-kernel@...r.kernel.org,
        steven.sistare@...cle.com, dhaval.giani@...cle.com,
        joelaf@...gle.com, vincent.guittot@...aro.org,
        morten.rasmussen@....com, eas-dev@...ts.linaro.org
Subject: Re: [RESEND PATCH] sched/fair: consider RT/IRQ pressure in
 select_idle_sibling



On 02/09/2018 07:46 AM, Dietmar Eggemann wrote:
> On 02/09/2018 01:53 PM, Peter Zijlstra wrote:
>> On Mon, Jan 29, 2018 at 03:27:09PM -0800, Rohit Jain wrote:
>
> [...]
>
>>> @@ -6173,8 +6183,15 @@ static int select_idle_cpu(struct task_struct 
>>> *p, struct sched_domain *sd, int t
>>>               return -1;
>>>           if (!cpumask_test_cpu(cpu, &p->cpus_allowed))
>>>               continue;
>>> +        if (idle_cpu(cpu)) {
>>> +            if (full_capacity(cpu)) {
>>> +                best_cpu = cpu;
>>> +                break;
>>> +            } else if (capacity_of(cpu) > best_cap) {
>>> +                best_cap = capacity_of(cpu);
>>> +                best_cpu = cpu;
>>> +            }
>>> +        }
>>
>> No need for the else. And you'll note you're once again inconsistent
>> with your previous self.
>>
>> But here I worry about big.little a wee bit. I think we're allowed big
>> and little cores on the same L3 these days, and you can't directly
>> compare capacity between them.
>>
>> Morten / Dietmar, any comments?
>
> Yes, for DynamIQ (big.little successor) systems, those cpus can have 
> different capacity_orig_of() values already.
>

OK, given that there are asymmetric capacities in L3 cores, we would
probably have something like the below(?) in select_idle_cpu:

           if (!cpumask_test_cpu(cpu, &p->cpus_allowed))
               continue;
+        if (idle_cpu(cpu) && !reduced_capacity(cpu))
+            break;