From: Qais Yousef qais.yousef@arm.com
commit 7226017ad37a888915628e59a84a2d1e57b40707 upstream.
When a new cgroup is created, the effective uclamp value wasn't updated with a call to cpu_util_update_eff() that looks at the hierarchy and update to the most restrictive values.
Fix it by ensuring to call cpu_util_update_eff() when a new cgroup becomes online.
Without this change, the newly created cgroup uses the default root_task_group uclamp values, which is 1024 for both uclamp_{min, max}, which will cause the rq to to be clamped to max, hence cause the system to run at max frequency.
The problem was observed on Ubuntu server and was reproduced on Debian and Buildroot rootfs.
By default, Ubuntu and Debian create a cpu controller cgroup hierarchy and add all tasks to it - which creates enough noise to keep the rq uclamp value at max most of the time. Imitating this behavior makes the problem visible in Buildroot too which otherwise looks fine since it's a minimal userspace.
Fixes: 0b60ba2dd342 ("sched/uclamp: Propagate parent clamps") Reported-by: Doug Smythies dsmythies@telus.net Signed-off-by: Qais Yousef qais.yousef@arm.com Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Tested-by: Doug Smythies dsmythies@telus.net Link: https://lore.kernel.org/lkml/000701d5b965%24361b6c60%24a2524520%24@net/ Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- kernel/sched/core.c | 6 ++++++ 1 file changed, 6 insertions(+)
--- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -7100,6 +7100,12 @@ static int cpu_cgroup_css_online(struct
if (parent) sched_online_group(tg, parent); + +#ifdef CONFIG_UCLAMP_TASK_GROUP + /* Propagate the effective uclamp value for the new group */ + cpu_util_update_eff(css); +#endif + return 0; }