linux-kernel - Re: [PATCH 4/6] futex: Use current->time_slack

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Date:	Thu, 12 Mar 2009 11:11:26 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Darren Hart <dvhltc@...ibm.com>
Cc:	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>,
	Rusty Russell <rusty@...tcorp.com.au>
Subject: Re: [PATCH 4/6] futex: Use current->time_slack_ns for rt tasks too

On Thu, 2009-03-12 at 00:55 -0700, Darren Hart wrote:
> RT tasks should set their timer slack to 0 on their own.  This patch removes
> the 'if (rt_task()) slack = 0;' block in futex_wait.

That wording makes me uncomfortable, either they do and this patch is
good, or they don't and you've now wrecked stuff :-)

A quick git grep suggests the latter..

> Build and boot tested on a 4 way Intel x86_64 workstation.  Passes basic
> pthread_mutex and PI tests out of ltp/testcases/realtime.
> 
> Signed-off-by: Darren Hart <dvhltc@...ibm.com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Ingo Molnar <mingo@...e.hu>
> Cc: Rusty Russell <rusty@...tcorp.com.au>
> ---
> 
>  kernel/futex.c |    7 ++-----
>  1 files changed, 2 insertions(+), 5 deletions(-)
> 
> diff --git a/kernel/futex.c b/kernel/futex.c
> index e149545..6579912 100644
> --- a/kernel/futex.c
> +++ b/kernel/futex.c
> @@ -1253,16 +1253,13 @@ retry:
>  		if (!abs_time)
>  			schedule();
>  		else {
> -			unsigned long slack;
> -			slack = current->timer_slack_ns;
> -			if (rt_task(current))
> -				slack = 0;
>  			hrtimer_init_on_stack(&t.timer,
>  					      clockrt ? CLOCK_REALTIME :
>  					      CLOCK_MONOTONIC,
>  					      HRTIMER_MODE_ABS);
>  			hrtimer_init_sleeper(&t, current);
> -			hrtimer_set_expires_range_ns(&t.timer, *abs_time, slack);
> +			hrtimer_set_expires_range_ns(&t.timer, *abs_time,
> +						     current->timer_slack_ns);
>  
>  			hrtimer_start_expires(&t.timer, HRTIMER_MODE_ABS);
>  			if (!hrtimer_active(&t.timer))
> 

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