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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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