linux-kernel - Re: [PATCH, v6 2/3] Implement timer slack notifier chain

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Message-ID: <alpine.LFD.2.00.1102141428080.26192@localhost6.localdomain6>
Date:	Mon, 14 Feb 2011 14:32:23 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	"Kirill A. Shutsemov" <kirill@...temov.name>
cc:	Paul Menage <menage@...gle.com>, Li Zefan <lizf@...fujitsu.com>,
	containers@...ts.linux-foundation.org,
	jacob.jun.pan@...ux.intel.com,
	Arjan van de Ven <arjan@...ux.intel.com>,
	linux-kernel@...r.kernel.org, Matt Helsley <matthltc@...ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-api@...r.kernel.org
Subject: Re: [PATCH, v6 2/3] Implement timer slack notifier chain

On Mon, 14 Feb 2011, Kirill A. Shutsemov wrote:

> From: Kirill A. Shutemov <kirill@...temov.name>
> 
> Process can change its timer slack using prctl(). Timer slack notifier
> call chain allows to react on such change or forbid it.

So we add a notifier call chain and more exports to allow what ?
 
> --- a/kernel/sys.c
> +++ b/kernel/sys.c
> @@ -1691,15 +1691,10 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
>  			error = perf_event_task_enable();
>  			break;
>  		case PR_GET_TIMERSLACK:
> -			error = current->timer_slack_ns;
> +			error = prctl_get_timer_slack();

  What's the point of replacing current->timer_slack_ns with a
  function which does exactly the same ?

> +long prctl_set_timer_slack(long timer_slack_ns)
> +{
> +	int err;
> +
> +	/* Reset timer slack to default value */
> +	if (timer_slack_ns <= 0) {
> +		current->timer_slack_ns = current->default_timer_slack_ns;
> +		return 0;

  That does not make any sense at all. Why is setting
  default_timer_slack_ns not subject to validation ? Why is it
  treaded seperately ?

> +	}
> +
> +	err = blocking_notifier_call_chain(&timer_slack_notify_list,
> +			timer_slack_ns, NULL);
> +	if (err == NOTIFY_DONE)
> +		current->timer_slack_ns = timer_slack_ns;
> +
> +	return notifier_to_errno(err);

Thanks,

	tglx
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