linux-kernel - Re: [RFC PATCH v1 1/2] sched: unified sched

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Date:	Wed, 25 Jan 2012 15:53:01 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>
Cc:	Vincent Guittot <vincent.guittot@...aro.org>,
	Indan Zupancic <indan@....nu>,
	Youquan Song <youquan.song@...el.com>,
	Ingo Molnar <mingo@...e.hu>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Jens Axboe <axboe@...nel.dk>
Subject: Re: [RFC PATCH v1 1/2] sched: unified sched_powersavings sysfs
 tunable

On Mon, 2012-01-16 at 21:52 +0530, Vaidyanathan Srinivasan wrote:
> +++ b/block/blk.h
> @@ -167,14 +167,15 @@ static inline int queue_congestion_off_threshold(struct request_queue *q)
>  static inline int blk_cpu_to_group(int cpu)
>  {
>         int group = NR_CPUS;
> -#ifdef CONFIG_SCHED_MC
> -       const struct cpumask *mask = cpu_coregroup_mask(cpu);
> -       group = cpumask_first(mask);
> -#elif defined(CONFIG_SCHED_SMT)
> -       group = cpumask_first(topology_thread_cpumask(cpu));
> +#ifdef CONFIG_SCHED_POWERSAVE
> +       if (smt_capable())
> +               group = cpumask_first(topology_thread_cpumask(cpu));
> +       else    
> +               group = cpumask_first(cpu_coregroup_mask(cpu));
>  #else
>         return cpu;
>  #endif
> +       /* Possible dead code?? */
>         if (likely(group < NR_CPUS))
>                 return group;
>         return cpu; 

After going, WTF is block doing! I had a closer look and this doesn't
seem right at all. The old code would use coregroup_mask when SCHED_MC
&& SCHED_SMT, the new code does something else.

Jens, what is this thing trying to do?

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