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SubjectRe: [PATCH] sched: don't allow rt_runtime_us to be zero for groups having rt tasks
On Wed, Feb 27, 2008 at 10:47:19PM +0100, Peter Zijlstra wrote:
>
> On Wed, 2008-02-27 at 18:54 +0530, Dhaval Giani wrote:
> > + struct task_struct *p;
> > + for_each_process(p) {
> > + if (rt_task(p) && rt_rq_of_se(&p->rt)->tg == tg)
> > + return 1;
> > + }
>
> This should be a do_each_thread() { } while_each_thread(); iteration
> loop;
>
> cgroups are thread oriented, not task.
>
> Sorry for missing this earlier.
>

Nice catch! Sorry for the mistake, corrected patch follows.
---
This patch checks if we can set the rt_runtime_us to 0. If there is a
realtime task in the group, we don't want to set the rt_runtime_us as 0
or bad things will happen.
Signed-off-by: Dhaval Giani <dhaval@linux.vnet.ibm.com>
---
kernel/sched.c | 17 +++++++++++++++++
1 files changed, 17 insertions(+)
Index: linux-2.6.25-rc3/kernel/sched.c
===================================================================
--- linux-2.6.25-rc3.orig/kernel/sched.c
+++ linux-2.6.25-rc3/kernel/sched.c
@@ -7960,6 +7960,17 @@ static int __rt_schedulable(struct task_
return total + to_ratio(period, runtime) < global_ratio;
}

+/* Must be called with tasklist_lock held */
+static inline int tg_has_rt_tasks(struct task_group *tg)
+{
+ struct task_struct *g, *p;
+ do_each_thread(g, p) {
+ if (rt_task(p) && rt_rq_of_se(&p->rt)->tg == tg)
+ return 1;
+ } while_each_thread(g, p);
+ return 0;
+}
+
int sched_group_set_rt_runtime(struct task_group *tg, long rt_runtime_us)
{
u64 rt_runtime, rt_period;
@@ -7971,6 +7982,11 @@ int sched_group_set_rt_runtime(struct ta
rt_runtime = rt_period;

mutex_lock(&rt_constraints_mutex);
+ read_lock(&tasklist_lock);
+ if (rt_runtime_us == 0 && tg_has_rt_tasks(tg)) {
+ err = -EINVAL;
+ goto unlock;
+ }
if (!__rt_schedulable(tg, rt_period, rt_runtime)) {
err = -EINVAL;
goto unlock;
@@ -7979,6 +7995,7 @@ int sched_group_set_rt_runtime(struct ta
rt_runtime = RUNTIME_INF;
tg->rt_runtime = rt_runtime;
unlock:
+ read_unlock(&tasklist_lock);
mutex_unlock(&rt_constraints_mutex);

return err;
--
regards,
Dhaval

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