Re: [patchlet] sched: fix rt throttle runtime borrowing

[Yong Zhang]

On Mon, Mar 7, 2011 at 4:21 PM, Mike Galbraith <efault@xxxxxx> wrote:
> Greetings,
>
> The RT throttle leaves a bit to be desired as a protection mechanism.
> With default settings, the thing won't save your bacon if you start a
> single hog as RT on SMP box, or if your normally sane app goes nuts.
>
> With the below, my box will limp along so I can kill the RT hog. ÂMay
> not be the best solution, but works for me.. modulo bustage I haven't
> noticed yet of course.
>
> sched: fix rt throttle runtime borrowing
>
> If allowed to borrow up to rt_period, the throttle has no effect on an out
> of control RT task, allowing it to consume 100% CPU indefinitely, blocking
> system critical SCHED_NORMAL threads indefinitely.

Yep.
I think it's helpful.

BTW, the comments(above diff calculation) in do_balance_runtime()
should be updated too :)

Thanks,
Yong

>
> Signed-off-by: Mike Galbraith <efault@xxxxxx>
>
> ---
> Âkernel/sched_rt.c | Â Â2 +-
> Â1 file changed, 1 insertion(+), 1 deletion(-)
>
> Index: linux-2.6/kernel/sched_rt.c
> ===================================================================
> --- linux-2.6.orig/kernel/sched_rt.c
> +++ linux-2.6/kernel/sched_rt.c
> @@ -354,7 +354,7 @@ static int do_balance_runtime(struct rt_
> Â Â Â Âweight = cpumask_weight(rd->span);
>
> Â Â Â Âraw_spin_lock(&rt_b->rt_runtime_lock);
> - Â Â Â rt_period = ktime_to_ns(rt_b->rt_period);
> + Â Â Â rt_period = ktime_to_ns(rt_b->rt_period) - 1;
> Â Â Â Âfor_each_cpu(i, rd->span) {
> Â Â Â Â Â Â Â Âstruct rt_rq *iter = sched_rt_period_rt_rq(rt_b, i);
> Â Â Â Â Â Â Â Âs64 diff;
>
>
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