On Fri, Jul 19, 2019 at 08:34:55AM +0200, Juri Lelli wrote: > On !CONFIG_RT_GROUP_SCHED configurations it is currently not possible to > move RT tasks between cgroups to which cpu controller has been attached; > but it is oddly possible to first move tasks around and then make them > RT (setschedule to FIFO/RR). > > E.g.: > > # mkdir /sys/fs/cgroup/cpu,cpuacct/group1 > # chrt -fp 10 $$ > # echo $$ > /sys/fs/cgroup/cpu,cpuacct/group1/tasks > bash: echo: write error: Invalid argument > # chrt -op 0 $$ > # echo $$ > /sys/fs/cgroup/cpu,cpuacct/group1/tasks > # chrt -fp 10 $$ > # cat /sys/fs/cgroup/cpu,cpuacct/group1/tasks > 2345 > 2598 > # chrt -p 2345 > pid 2345's current scheduling policy: SCHED_FIFO > pid 2345's current scheduling priority: 10 > > Also, as Michal noted, it is currently not possible to enable cpu > controller on unified hierarchy with !CONFIG_RT_GROUP_SCHED (if there > are any kernel RT threads in root cgroup, they can't be migrated to the > newly created cpu controller's root in cgroup_update_dfl_csses()). > > Existing code comes with a comment saying the "we don't support RT-tasks > being in separate groups". Such comment is however stale and belongs to > pre-RT_GROUP_SCHED times. Also, it doesn't make much sense for > !RT_GROUP_ SCHED configurations, since checks related to RT bandwidth > are not performed at all in these cases. > > Make moving RT tasks between cpu controller groups viable by removing > special case check for RT (and DEADLINE) tasks. I have very vague memories of there being a matching test in sched_setscheduler(), but clearly that's no longer there. Thanks! > Signed-off-by: Juri Lelli <juri.lelli@xxxxxxxxxx> > Reviewed-by: Michal Koutný <mkoutny@xxxxxxxx> > Acked-by: Tejun Heo <tj@xxxxxxxxxx> > --- > v1 -> v2: added comment about unified hierachy in changelog (Michal) > collected acks/reviews > --- > kernel/sched/core.c | 4 ---- > 1 file changed, 4 deletions(-) > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index fa43ce3962e7..be041dc7d313 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -6934,10 +6934,6 @@ static int cpu_cgroup_can_attach(struct cgroup_taskset *tset) > #ifdef CONFIG_RT_GROUP_SCHED > if (!sched_rt_can_attach(css_tg(css), task)) > return -EINVAL; > -#else > - /* We don't support RT-tasks being in separate groups */ > - if (task->sched_class != &fair_sched_class) > - return -EINVAL; > #endif > /* > * Serialize against wake_up_new_task() such that if its > -- > 2.17.2 >
