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To: Ingo Molnar <mingo@elte.hu>
cc: Florian Schmidt <mista.tapas@gmx.net>, Rui Nuno Capela <rncbc@rncbc.org>,
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       Esben Nielsen <simlo@phys.au.dk>
Subject: Re: [patch] Real-Time Preemption, -RT-2.6.10-rc2-mm2-V0.7.30-2 
In-reply-to: Your message of "Wed, 01 Dec 2004 15:37:38 +0100."
             <20041201143738.GA12563@elte.hu> 
Date: Wed, 01 Dec 2004 09:56:37 -0500
From: Paul Davis <paul@linuxaudiosystems.com>
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>in kernels -V0.7.30-9 or later they are RT-safe when PREEMPT_RT is
>enabled.

thats good to hear.

>also, the problem is that jackd uses _named_ fifos, which are tied to
>the raw FS and might trigger journalling activities. Normal pipes
>(unnamed fifos) would not cause such problems. Would it be possible to
>change jackd to use a pair of pipes, instead of a fifo?

i.e. pipe(2) rather than mkfifo(2) ?

it would be a complete pain because the pipes have to be
"discoverable" across processes. we would have to do fd passing, which
is still really quite ugly in linux (and other *nix systems). it
would quite difficult, though not impossible.

>> [...] i have outlined an idea to ingo that florian and i cooked up one
>> evening on IRC that would provide true RT-safe IPC mechanisms, but as
>> i recall, he didn't seem to think that much of it :)
>
>actually, my answer (sent on Nov 1) was:
>
>> futexes are nearly lock-free. [and even those locks are short-held so
>> combined with priority-inheritance they should be lockfree in
>> essence.] Would futexes suit your purposes?
>
>to which suggestion i got no reply yet :-)

i am still trying to find the time to investigate futexes. they seem
close to the desired object, but have a slightly more general semantic
than i can fit into my head right now;)

--p