linux-kernel - Re: [PATCH v6 5/9] x86/sysctl: Add sysctl for ITMT scheduling feature

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Date:   Wed, 26 Oct 2016 12:49:36 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Tim Chen <tim.c.chen@...ux.intel.com>
cc:     rjw@...ysocki.net, mingo@...hat.com, bp@...e.de, x86@...nel.org,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-acpi@...r.kernel.org, peterz@...radead.org, jolsa@...hat.com,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
Subject: Re: [PATCH v6 5/9] x86/sysctl: Add sysctl for ITMT scheduling
 feature

On Thu, 20 Oct 2016, Tim Chen wrote:
> +static int sched_itmt_update_handler(struct ctl_table *table, int write,
> +			      void __user *buffer, size_t *lenp, loff_t *ppos)

Please align the arguments proper

static int
sched_itmt_update_handler(struct ctl_table *table, int write,
			  void __user *buffer, size_t *lenp, loff_t *ppos)

> +{
> +	int ret;
> +	unsigned int old_sysctl;

	unsigned int old_sysctl;
	int ret;

Please. It's way simpler to read.

> -void sched_set_itmt_support(void)
> +int sched_set_itmt_support(void)
>  {
>  	mutex_lock(&itmt_update_mutex);
>  
> +	if (sched_itmt_capable) {
> +		mutex_unlock(&itmt_update_mutex);
> +		return 0;
> +	}
> +
> +	itmt_sysctl_header = register_sysctl_table(itmt_root_table);
> +	if (!itmt_sysctl_header) {
> +		mutex_unlock(&itmt_update_mutex);
> +		return -ENOMEM;
> +	}
> +
>  	sched_itmt_capable = true;
>  
> +	/*
> +	 * ITMT capability automatically enables ITMT
> +	 * scheduling for small systems (single node).
> +	 */
> +	if (topology_num_packages() == 1)
> +		sysctl_sched_itmt_enabled = 1;

I really hate this. This is policy and the kernel should not impose
policy. Why would I like to have this enforced on my single socket XEON
server?

> +	if (sysctl_sched_itmt_enabled) {

Why would sysctl_sched_itmt_enabled be true at this point, aside of the
above policy imposement?

Thanks,

	tglx