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

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Date:   Fri, 9 Feb 2018 16:46:53 +0100
From:   Dietmar Eggemann <dietmar.eggemann@....com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Rohit Jain <rohit.k.jain@...cle.com>
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 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.