Hi Philippe,

I have attached this patch to my application. So far it looks really good.
However, I leave my test running to be sure that it works.



> On Fri, 2007-07-20 at 14:16 +0200, Philippe Gerum wrote: 
> > On Fri, 2007-07-20 at 13:54 +0200, M. Koehrer wrote:
> > > Hi Philippe,
> > > I left my test running for a couple of hours - no freeze so far... 
> > > 
> > > However, I have to do some other stuff on this machine, I have to stop
> the test now...
> > > 
> > 
> > Ok, thanks for the feedback. I will send an extended patch later today,
> > so that you could test it on a longer period when you see fit.
> It took me a bit longer than expected, but here is a patch which
> addresses all the pending issues with RPI, hopefully (applies against
> 2.3.1 stock).
> The good thing about Jan grumbling at me, is that this usually makes me
> look at the big picture anew. And the RPI picture was not that nice,
> that's a fact.
> Beside the locking sequence issue, the ex-aequo #1 problem was that CPU
> migration of Linux tasks causing a RPI boost had some very nasty
> side-effects on RPI management, and would create all sort of funky
> situations I'm too shameful to talk about, except under the generic term
> of "horrendous mess".
> Now, regarding the deadlock issue, suppressing the RPI-specific locking
> entirely would have been the best solution, but unfortunately, the
> migration scheme makes this out of reach, at least without resorting to
> some hairy and likely unreliable implementation. Therefore, the solution
> I came with consists of making the RPI lock a per-cpu thing, so that
> most RPI routines are actually grabbing a _local_ lock wrt the current
> CPU, those routines being allowed hold the nklock as they wish. When
> some per-CPU RPI lock is accessed from a remote CPU, it is guaranteed
> that _no nklock_ may be held nested. Actually, the remote case only
> occurs once, in rpi_clear_remote(), and all its callers are guaranteed
> to be nklock-free (a debug assertion even enforces that).
> For the migration issue, the RPI transitions have been ironed out to
> make sure we deal properly with all the subtleties of the Linux load
> balancer.
> Mathias, please let me know if the attached patch improves the situation
> on your side.
> -- 
> Philippe.

Mathias Koehrer

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