Messages in this thread | | | Subject | Re: [RFC 1/6] sched: Add nice value change notifier | From | Tvrtko Ursulin <> | Date | Fri, 1 Oct 2021 10:04:53 +0100 |
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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
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