Messages in this thread | | | Subject | Re: [PATCH 6/6] Makes procs file writable to move all threads by tgid at once | From | Peter Zijlstra <> | Date | Thu, 06 Aug 2009 13:39:21 +0200 |
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On Thu, 2009-08-06 at 04:24 -0700, Paul Menage wrote: > On Thu, Aug 6, 2009 at 4:02 AM, Peter Zijlstra<a.p.zijlstra@chello.nl> wrote: > > > > Taking that many locks in general, some apps (JVM based usually) tend to > > be thread heavy and can easily have hundreds of them, even on relatively > > Oh, I'm well aware that apps can be heavily multi-threaded - we have > much worse cases at Google. > > > > > Now that's not real nice is it ;-) > > Not particularly - but who exactly is going to be moving processes > with thousands of threads between cgroups on a lockdep-enabled debug > kernel?
All it takes are: 8 or 48 (or soon 2048) depending on your particular annotation. I might and then I'd have to come and kick you ;-)
Really, lockdep not being able to deal with something is a strong indication that you're doing something wonky.
Stronger, you can even do wonky things which lockdep thinks are absolutely fine.
And doing wonky things should be avoided :-)
Luckily we seem to have found a sensible solution.
> What benefits does the additional complexity of SRCU give, over the > simple solution of putting an rwsem in the same cache line as > sighand->count ?
I said:
> Then again, clone() might already serialize on the process as a whole > (not sure though, Oleg/Ingo?), in which case you can indeed take a > process wide lock.
Which looking up sighand->count seems to be the case:
static int copy_sighand(unsigned long clone_flags, struct task_struct *tsk) { struct sighand_struct *sig;
if (clone_flags & CLONE_SIGHAND) { atomic_inc(¤t->sighand->count); return 0; }
So yes, putting a rwsem in there sounds fine, you're already bouncing it.
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