24 Jun
2009
24 Jun
'09
1:25 a.m.
On Mon, 2009-06-22 at 15:14 +0200, Lennart Poettering wrote:
On Sun, 21.06.09 20:58, Fernando Lopez-Lezcano
(nando(a)ccrma.Stanford.EDU) wrote:
I'm talking about the rt kernels specifically. In that context users
don't have a real choice as to what they get to run and the meaning of
legacy is different (I understand you may not care because of the target
audience of PA, but then again the RealtimeKit is being proposed as a
generic solution for access to rt scheduling).
If the rt patch does not catch up fast enough then I may need to run a <
2.6.31 kernel (whatever is available at the time) in Fedora 12 when it
is released, hardly a legacy distro :-)
(maybe unlikely, but it would not be the first time rt development
stalls for a looong time and you can't run the latest and greatest - not
complaining, just a fact)
Again, the worst thing that happens is that you need to bump
RLIMIT_RTPRIO for your user, as you always did. rtkit doesn't take
that away.
Summary:
Kernel that lacks SCHED_RESET_ON_FORK: RLIMIT_RTPRIO is what matters.
Kernel that has SCHED_RESET_ON_FORK: RLIMIT_RTPRIO still matters when
it is set, rtkit is used as fallback.
I understand.
The question is relevant, I think, as the kernels that
I use (Planet
CCRMA) are the rt patched kernels, currently limited to 2.6.29.5 (I
think Thomas and the rt gang are working on 2.6.30, I imagine 2.6.31
support is still far in the future).
Dunno. I disagree. The primary objective for rtkit is to be able to
run media applications as RT by default, out-of-the-box. I doubt that
this feature matters for legacy distros/kernels. Also note that supporting rtkit often enough
doesn't add a build-time
dep to you application and the runtime dependency is very soft too: if
it isn't found it's not used, that's all.
Let's assume for a moment that when rtkit becomes part of Fedora the rt
kernel patch has not caught up to 2.6.31, would you consider changing
the behavior so that if the kernel does not have SCHED_RESET_ON_FORK
(ie: it is older than 2.6.31) rtkit would still grant rt if the other
conditions are met? Or add a boot time configuration to be able to do
that?
That would mean that _temporarily_ older rt kernels (and jack users that
prefer or need to use them) would be able to use the same out of the box
rt granting mechanism as the rest of Fedora.
-- Fernando