From: Juri Lelli juri.lelli@redhat.com
[ Upstream commit a07db5c0865799ebed1f88be0df50c581fb65029 ]
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.
Signed-off-by: Juri Lelli juri.lelli@redhat.com Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Reviewed-by: Michal Koutný mkoutny@suse.com Reviewed-by: Daniel Bristot de Oliveira bristot@redhat.com Acked-by: Tejun Heo tj@kernel.org Cc: Linus Torvalds torvalds@linux-foundation.org Cc: Peter Zijlstra peterz@infradead.org Cc: Thomas Gleixner tglx@linutronix.de Cc: lizefan@huawei.com Cc: longman@redhat.com Cc: luca.abeni@santannapisa.it Cc: rostedt@goodmis.org Link: https://lkml.kernel.org/r/20190719063455.27328-1-juri.lelli@redhat.com Signed-off-by: Ingo Molnar mingo@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/sched/core.c | 4 ---- 1 file changed, 4 deletions(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 0e70bfeded7fd..d81bcc6362fff 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -8339,10 +8339,6 @@ 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 } return 0;