linux-kernel - Re: [RFCv2 5/6] sched/fair: Tune task wake-up logic to pack jitter tasks

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Date:   Wed, 15 May 2019 18:43:00 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Parth Shah <parth@...ux.ibm.com>
Cc:     linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        mingo@...hat.com, dietmar.eggemann@....com, dsmythies@...us.net
Subject: Re: [RFCv2 5/6] sched/fair: Tune task wake-up logic to pack jitter
 tasks

On Wed, May 15, 2019 at 07:23:21PM +0530, Parth Shah wrote:
> @@ -6704,6 +6773,31 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
>  	return -1;
>  }
>  
> +#ifdef CONFIG_SCHED_SMT
> +/*
> + * Select all tasks of type 1(jitter) for task packing
> + */
> +static int turbosched_select_idle_sibling(struct task_struct *p, int prev_cpu,
> +					  int target)
> +{
> +	int new_cpu;
> +
> +	if (unlikely(task_group(p)->turbo_sched_enabled)) {

So if you build without cgroups, this is a NULL dereference.

Also, this really should not be group based.

> +		new_cpu = select_non_idle_core(p, prev_cpu);
> +		if (new_cpu >= 0)
> +			return new_cpu;
> +	}
> +
> +	return select_idle_sibling(p, prev_cpu, target);
> +}
> +#else