Date: Tue, 23 Nov 2004 10:21:52 +0100
From: Ingo Molnar <mingo@elte.hu>
To: john cooper <john.cooper@timesys.com>
Cc: "Bill Huey (hui)" <bhuey@lnxw.com>, Esben Nielsen <simlo@phys.au.dk>,
       linux-kernel@vger.kernel.org
Subject: Re: Priority Inheritance Test (Real-Time Preemption)
Message-ID: <20041123092152.GA5061@elte.hu>
References: <Pine.OSF.4.05.10411212107240.29110-100000@da410.ifa.au.dk> <20041122092302.GA7210@nietzsche.lynx.com> <41A1F4B2.10401@timesys.com> <20041122152452.GA2036@elte.hu> <41A2902A.5050308@timesys.com>
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* john cooper <john.cooper@timesys.com> wrote:

> >>I'd hazard a guess the reason existing implementations do not do this
> >>type of dependency-chain closure is the complexity of a general
> >>approach. [...]
> >
> >
> >please take a look at the latest patch, it is i believe handling all the
> >cases correctly. It certainly appears to solve the cases uncovered by
> >pi_test.
> 
> Yes I see where you are walking the dependency chain
> in pi_setprio().  But this is under the global spinlock
> 'pi_lock'.
> 
> My earlier comment was of the difficulty to establish fine
> grained locking, [...]

the issues raised in the paper and in this thread were much more
fundamental than SMP-scalability. Considering the costs of a hard-RT
mutex approach itself i dont think SMP-scalability is a primary issue
right now.

> [...]  However I'd offer there is more concurrency possible in this
> design.

yeah, most likely - but correctness comes first. SMP scalability is
something that can be done later.

	Ingo
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