Re: [PATCH v14 5/6] sched/core: uclamp: Update CPU's refcount on TG's clamp changes
From: Peter Zijlstra <peterz@infradead.org>
Date: 2019-08-30 09:48:46
Also in:
cgroups, linux-pm, lkml
On Thu, Aug 22, 2019 at 02:28:10PM +0100, Patrick Bellasi wrote:
quoted hunk ↗ jump to hunk
diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 04fc161e4dbe..fc2dc86a2abe 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c@@ -1043,6 +1043,57 @@ static inline void uclamp_rq_dec(struct rq *rq, struct task_struct *p) uclamp_rq_dec_id(rq, p, clamp_id); } +static inline void +uclamp_update_active(struct task_struct *p, unsigned int clamp_id) +{ + struct rq_flags rf; + struct rq *rq; + + /* + * Lock the task and the rq where the task is (or was) queued. + * + * We might lock the (previous) rq of a !RUNNABLE task, but that's the + * price to pay to safely serialize util_{min,max} updates with + * enqueues, dequeues and migration operations. + * This is the same locking schema used by __set_cpus_allowed_ptr(). + */ + rq = task_rq_lock(p, &rf);
Since modifying cgroup parameters is priv only, this should be OK I suppose. Priv can already DoS the system anyway.
+ /* + * Setting the clamp bucket is serialized by task_rq_lock(). + * If the task is not yet RUNNABLE and its task_struct is not + * affecting a valid clamp bucket, the next time it's enqueued, + * it will already see the updated clamp bucket value. + */ + if (!p->uclamp[clamp_id].active) + goto done; + + uclamp_rq_dec_id(rq, p, clamp_id); + uclamp_rq_inc_id(rq, p, clamp_id); + +done:
I'm thinking that:
if (p->uclamp[clamp_id].active) {
uclamp_rq_dec_id(rq, p, clamp_id);
uclamp_rq_inc_id(rq, p, clamp_id);
}
was too obvious? ;-)
+ + task_rq_unlock(rq, p, &rf); +}