Messages in this thread | | | Subject | Re: [PATCH] sched: allow preempt notifiers to self-unregister. | From | Peter Zijlstra <> | Date | Fri, 16 Dec 2011 18:33:07 +0100 |
| |
On Fri, 2011-12-16 at 18:25 +0100, Pierre Habouzit wrote: > On Fri, Dec 16, 2011 at 06:09:45PM +0100, Peter Zijlstra wrote: > > On Fri, 2011-12-16 at 17:15 +0100, Pierre Habouzit wrote: > > > > > As a background, this need is because I have some kind of module code > > > that uses this facility to evaluate how many of a group of threads are > > > concurrently running (to regulate a pool of threads). > > > > Typically such stuff is only merged along with whomever uses it. > > Well for now I'm just toying with it, it's nowhere nead to be ready to > be even shown without me having to bury my head from shame ;)
:-) no worries just keep something like this along until you're ready..
> > > Hence I install those callbacks for the thread registering themselves > > > and want to keep them until the thread dies. Sadly I have no way to > > > unregister those callbacks right now, but for horrible hacks (involving > > > private delayed queues processed regularly walked to kfree() the > > > structures referencing pids that are dead, urgh). > > > > kfree_rcu() is the 'normal' way to cheat your way out of this. > > Hmm, if when I'm scheduled "out" with the TASK_DEAD bit set, am I sure > the _in/_out callback will never ever be called again?
Yep.
> It experimentally seems that the answer is yes, but I'm not familiar > enough with the scheduler to be a 100% sure. If yes then kfree_rcu is > just fine indeed and I don't need the patch, at all. > > If it's not "sure" then I assume I can probably use call_rcu() but that
kfree_rcu() is a convenient macro wrapped around call_rcu().
> looks like a total overkill for something that can be fully avoided with > my patch, which incidentally, doesn't slow the typical sched path (there > should be no callbacks and the _safe iterator exits as fast as the non > safe iterator).
Ah, you're right, I thought it frobbed the extra variable too, but looking at it it only does that when there's anything on the list.
| |