On Tue, Aug 06, 2019 at 17:11:53 +0100, Michal Koutný wrote... > On Fri, Aug 02, 2019 at 10:08:49AM +0100, Patrick Bellasi <patrick.bellasi@xxxxxxx> wrote: >> @@ -7095,6 +7149,7 @@ static ssize_t cpu_uclamp_write(struct kernfs_open_file *of, char *buf, >> if (req.ret) >> return req.ret; >> >> + mutex_lock(&uclamp_mutex); >> rcu_read_lock(); >> >> tg = css_tg(of_css(of)); >> @@ -7107,7 +7162,11 @@ static ssize_t cpu_uclamp_write(struct kernfs_open_file *of, char *buf, >> */ >> tg->uclamp_pct[clamp_id] = req.percent; >> >> + /* Update effective clamps to track the most restrictive value */ >> + cpu_util_update_eff(of_css(of)); >> + >> rcu_read_unlock(); >> + mutex_unlock(&uclamp_mutex); > Following my remarks to "[PATCH v13 1/6] sched/core: uclamp: Extend > CPU's cgroup", I wonder if the rcu_read_lock() couldn't be moved right > before cpu_util_update_eff(). And by extension rcu_read_(un)lock could > be hidden into cpu_util_update_eff() closer to its actual need. Well, if I've got correctly your comment in the previous message, I would say that at this stage we don't need RCU looks at all. Reason being that cpu_util_update_eff() gets called only from cpu_uclamp_write() which is from an ongoing write operation on a cgroup attribute and thus granted to be available. We will eventually need to move the RCU look only down the stack when uclamp_update_active_tasks() gets called to update the RUNNABLE tasks on a RQ... or perhaps we don't need them since we already get the task_rq_lock() for each task we visit. Is that correct? Cheers, Patrick -- #include <best/regards.h> Patrick Bellasi
