Hi Peter,
On 30/09/2021 19:33, Peter Zijlstra wrote:
On Thu, Sep 30, 2021 at 06:15:47PM +0100, Tvrtko Ursulin wrote:
void set_user_nice(struct task_struct *p, long nice)
{
bool queued, running;
- int old_prio;
+ int old_prio, ret;
struct rq_flags rf;
struct rq *rq;
@@ -6913,6 +6945,9 @@ void set_user_nice(struct task_struct *p, long nice)
*/
p->sched_class->prio_changed(rq, p, old_prio);
+ ret = atomic_notifier_call_chain(&user_nice_notifier_list, nice, p);
+ WARN_ON_ONCE(ret != NOTIFY_DONE);
+
out_unlock:
task_rq_unlock(rq, p, &rf);
}
No, we're not going to call out to exported, and potentially unbounded,
functions under scheduler locks.
Agreed, that's another good point why it is even more hairy, as I have
generally alluded in the cover letter.
Do you have any immediate thoughts on possible alternatives?
Like for instance if I did a queue_work from set_user_nice and then ran
a notifier chain async from a worker? I haven't looked at yet what
repercussion would that have in terms of having to cancel the pending
workers when tasks exit. I can try and prototype that and see how it
would look.
There is of course an example ioprio which solves the runtime
adjustments via a dedicated system call. But I don't currently feel that
a third one would be a good solution. At least I don't see a case for
being able to decouple the priority of CPU and GPU and computations.
Have I opened a large can of worms? :)
Regards,
Tvrtko
