On 2016-09-10 08:17:13 [+0200], Thomas Gleixner wrote:
> On Thu, 8 Sep 2016, Sebastian Andrzej Siewior wrote:
> > + if (parent == dentry) {
> > + /* the task with the highest priority won't schedule */
> > + r = cond_resched();
> > + if (!r && (rt_task(current) || dl_task(current)))
>
> That's wrong because a non RT task will just spin until its time slice is
> up. Wasted cycles for nothing.
>
> Ideally we make spinning conditional on
>
> !on_cpu(dentry->lock->owner)
>
> That would avoid going to sleep if the owner runs on another cpu. We have
> no mechanism for that, but I think it'd be worth to think about one.
something like
|#ifdef CONFIG_SMP
| task_running(task_rq(lock_owner), lock_owner))
|#else
| 1)
|#endif
| cpu_chill();
the lock_owner is tricky because we have two locks: inode->i_lock and
parent->d_lock. So we would have to do the same lookup, like
dentry_kill() is doing, and check both in worth case.
Sebastian
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