linux-kernel - Re: [PATCH 2/2] sched/fair: Improve the for loop in select_idle

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Date:   Mon, 11 Feb 2019 15:56:59 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] sched/fair: Improve the for loop in
 select_idle_core()

On 11-02-19, 10:30, Peter Zijlstra wrote:
> On Thu, Feb 07, 2019 at 04:16:06PM +0530, Viresh Kumar wrote:
> > @@ -6081,10 +6082,14 @@ static int select_idle_core(struct task_struct *p, struct sched_domain *sd, int
> >  	for_each_cpu_wrap(core, cpus, target) {
> >  		bool idle = true;
> >  
> > -		for_each_cpu(cpu, cpu_smt_mask(core)) {
> > -			cpumask_clear_cpu(cpu, cpus);
> > -			if (!available_idle_cpu(cpu))
> > +		smt = cpu_smt_mask(core);
> > +		cpumask_andnot(cpus, cpus, smt);
> 
> So where the previous code was like 1-2 stores, you just added 16.

Is the max number of possible threads per core just 2? That's what I
read just now and I wasn't aware of that earlier. This commit doesn't
improve anything then. Sorry for the noise.

-- 
viresh