linux-kernel - Re: [RFC PATCH 07/13] sched: Add core wide task selection and scheduling.

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Message-ID: <1e587d48-2e61-e425-81cf-d304e13c91d4@linux.intel.com>
Date:   Thu, 16 Apr 2020 16:32:28 -0700
From:   Tim Chen <tim.c.chen@...ux.intel.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        vpillai <vpillai@...italocean.com>
Cc:     Nishanth Aravamudan <naravamudan@...italocean.com>,
        Julien Desfossez <jdesfossez@...italocean.com>,
        mingo@...nel.org, tglx@...utronix.de, pjt@...gle.com,
        torvalds@...ux-foundation.org, linux-kernel@...r.kernel.org,
        fweisbec@...il.com, keescook@...omium.org, kerrnel@...gle.com,
        Phil Auld <pauld@...hat.com>, Aaron Lu <aaron.lwe@...il.com>,
        Aubrey Li <aubrey.intel@...il.com>, aubrey.li@...ux.intel.com,
        Valentin Schneider <valentin.schneider@....com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Joel Fernandes <joelaf@...gle.com>, joel@...lfernandes.org,
        Aaron Lu <aaron.lu@...ux.alibaba.com>
Subject: Re: [RFC PATCH 07/13] sched: Add core wide task selection and
 scheduling.



On 4/14/20 6:35 AM, Peter Zijlstra wrote:
> On Wed, Mar 04, 2020 at 04:59:57PM +0000, vpillai wrote:
>> +static struct task_struct *
>> +pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
>> +{
>> +	struct task_struct *next, *max = NULL;
>> +	const struct sched_class *class;
>> +	const struct cpumask *smt_mask;
>> +	int i, j, cpu;
>> +	bool need_sync = false;
> 
> AFAICT that assignment is superfluous. Also, you violated the inverse
> x-mas tree.
> 
>> +
>> +	cpu = cpu_of(rq);
>> +	if (cpu_is_offline(cpu))
>> +		return idle_sched_class.pick_next_task(rq);
> 
> Are we actually hitting this one?
> 

I did hit this race when I was testing taking cpu offline and online,
which prompted the check of cpu being offline.

Tim