Re: [PATCH 4/6] futex: Use current->time_slack_ns for rt tasks too

Peter Zijlstra
2009-03-12T10:11:55Z

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@us.ibm.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Ingo Molnar <mingo@elte.hu>
> Cc: Rusty Russell <rusty@rustcorp.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))
>