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Subject: Re: [RFC PATCH 07/13] sched: Add core wide task selection and
 scheduling.
To:     Peter Zijlstra <peterz@infradead.org>,
        vpillai <vpillai@digitalocean.com>
Cc:     Nishanth Aravamudan <naravamudan@digitalocean.com>,
        Julien Desfossez <jdesfossez@digitalocean.com>,
        mingo@kernel.org, tglx@linutronix.de, pjt@google.com,
        torvalds@linux-foundation.org, linux-kernel@vger.kernel.org,
        fweisbec@gmail.com, keescook@chromium.org, kerrnel@google.com,
        Phil Auld <pauld@redhat.com>, Aaron Lu <aaron.lwe@gmail.com>,
        Aubrey Li <aubrey.intel@gmail.com>, aubrey.li@linux.intel.com,
        Valentin Schneider <valentin.schneider@arm.com>,
        Mel Gorman <mgorman@techsingularity.net>,
        Pawan Gupta <pawan.kumar.gupta@linux.intel.com>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Joel Fernandes <joelaf@google.com>, joel@joelfernandes.org,
        Aaron Lu <aaron.lu@linux.alibaba.com>
References: <cover.1583332764.git.vpillai@digitalocean.com>
 <e942da7fd881977923463f19648085c1bfaa37f8.1583332765.git.vpillai@digitalocean.com>
 <20200414133559.GT20730@hirez.programming.kicks-ass.net>
From:   Tim Chen <tim.c.chen@linux.intel.com>
Message-ID: <1e587d48-2e61-e425-81cf-d304e13c91d4@linux.intel.com>
Date:   Thu, 16 Apr 2020 16:32:28 -0700
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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