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SubjectRe: [PATCH] sched: rt-bandwidth disable fixes
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On Mon, 2008-08-18 at 12:47 +0200, Peter Zijlstra wrote:
> On Mon, 2008-08-18 at 00:15 +0200, Dario Faggioli wrote:
> > On Sat, 2008-08-16 at 23:29 +0200, Stefani Seibold wrote:
> > > After disabling kernel support for "Group CPU scheduler" and applying
> > > 'echo -1 > /proc/sys/kernel/sched_rt_runtime_us' the behaviour is as
> > > expected.
>
> > > So the problem is located first in the new sched_rt_runtime_us default
> > > value and second in the "Group CPU scheduler".
> > Well, if you have group scheduling configured I think you should do both
> > # echo -1 > /proc/sys/kernel/sched_rt_runtime_us
> > # echo -1 > /dev/cgroup/cpu.rt_runtime_us
> >
> > if /dev/cgroup is the mount point of the cgroup file system.
> >
> > In situations like the one you are describing, this worked for me...
> > Hope that it also helps you! :-)
>
> Ah, right - I knew I was forgetting something..
>
> (compile tested only)

Right - I knew I was forgetting something... this patch forgets:

- to allow tasks to groups that have a 0 limit when bandwidth control
is disabled
- deal with the trouble that gets us in on enabling it again after
that happens.

So, please skip this patch for now..

> ---
> Subject: sched: rt-bandwidth disable fixes
> From: Peter Zijlstra <a.p.zijlstra@chello.nl>
> Date: Mon Aug 18 12:39:07 CEST 2008
>
> Currently there is no way to revert to the classical behaviour if
> RT_GROUP_SCHED is set. Fix this by introducing rt_bandwidth_enabled(),
> which will turn off all the bandwidth accounting if sched_rt_runtime_us
> is set to a negative value.
>
> Also fix a bug where we would still increase the used time when the limit
> would be set to RUNTIME_INF - causing a long throttle period once it would
> be lowered.
>
> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
> ---
> kernel/sched.c | 9 ++++++++-
> kernel/sched_rt.c | 16 +++++++++-------
> 2 files changed, 17 insertions(+), 8 deletions(-)
>
> Index: linux-2.6/kernel/sched.c
> ===================================================================
> --- linux-2.6.orig/kernel/sched.c
> +++ linux-2.6/kernel/sched.c
> @@ -204,11 +204,13 @@ void init_rt_bandwidth(struct rt_bandwid
> rt_b->rt_period_timer.cb_mode = HRTIMER_CB_IRQSAFE_NO_SOFTIRQ;
> }
>
> +static inline int rt_bandwidth_enabled(void);
> +
> static void start_rt_bandwidth(struct rt_bandwidth *rt_b)
> {
> ktime_t now;
>
> - if (rt_b->rt_runtime == RUNTIME_INF)
> + if (rt_bandwidth_enabled() && rt_b->rt_runtime == RUNTIME_INF)
> return;
>
> if (hrtimer_active(&rt_b->rt_period_timer))
> @@ -839,6 +841,11 @@ static inline u64 global_rt_runtime(void
> return (u64)sysctl_sched_rt_runtime * NSEC_PER_USEC;
> }
>
> +static inline int rt_bandwidth_enabled(void)
> +{
> + return sysctl_sched_rt_runtime >= 0;
> +}
> +
> #ifndef prepare_arch_switch
> # define prepare_arch_switch(next) do { } while (0)
> #endif
> Index: linux-2.6/kernel/sched_rt.c
> ===================================================================
> --- linux-2.6.orig/kernel/sched_rt.c
> +++ linux-2.6/kernel/sched_rt.c
> @@ -386,7 +386,7 @@ static int do_sched_rt_period_timer(stru
> int i, idle = 1;
> cpumask_t span;
>
> - if (rt_b->rt_runtime == RUNTIME_INF)
> + if (!rt_bandwidth_enabled() || rt_b->rt_runtime == RUNTIME_INF)
> return 1;
>
> span = sched_rt_period_mask();
> @@ -438,9 +438,6 @@ static int sched_rt_runtime_exceeded(str
> {
> u64 runtime = sched_rt_runtime(rt_rq);
>
> - if (runtime == RUNTIME_INF)
> - return 0;
> -
> if (rt_rq->rt_throttled)
> return rt_rq_throttled(rt_rq);
>
> @@ -487,13 +484,18 @@ static void update_curr_rt(struct rq *rq
> curr->se.exec_start = rq->clock;
> cpuacct_charge(curr, delta_exec);
>
> + if (!rt_bandwidth_enabled())
> + return;
> +
> for_each_sched_rt_entity(rt_se) {
> rt_rq = rt_rq_of_se(rt_se);
>
> spin_lock(&rt_rq->rt_runtime_lock);
> - rt_rq->rt_time += delta_exec;
> - if (sched_rt_runtime_exceeded(rt_rq))
> - resched_task(curr);
> + if (sched_rt_runtime(rt_rq) != RUNTIME_INF) {
> + rt_rq->rt_time += delta_exec;
> + if (sched_rt_runtime_exceeded(rt_rq))
> + resched_task(curr);
> + }
> spin_unlock(&rt_rq->rt_runtime_lock);
> }
> }
>
>
> --
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