There's no such thing as a hard kernel. [sarcasm]But that means Ubuntu was wrong, or they lied! I'm shocked! Everything on the internets is true![/sarcasm]
Thanks for straitening that out for me. I had emailed the maintainer at Ubuntu but never got a response. (maybe my emails give offensive order because I haven't heard from anyone at RedHat lately either) Sigh... I'm bummed to hear that progress on this may be halting. I wish there was someone to bully to get some traction or funding for this. Sigh... On Tue Dec 30 2014 at 10:07:47 PM Fernando Lopez-Lezcano < [email protected]> wrote: > On 11/19/2014 08:01 AM, Brian Monroe wrote: > > On Thu Nov 13 2014 at 12:28:27 PM Jeff Sandys <[email protected] > > <mailto:[email protected]>> wrote: > > > > Real Time Kernels are available from PlanetCCRMA: > > http://ccrma.stanford.edu/planetccrma/mirror/fedora/ > linux/planetcore/20/x86_64/repoview/kernel-rt.html > > > > There are concerns about the implementation of Real Time Kernel as > > expressed in the Musician's Guide: > > http://docs.fedoraproject.org/en-US/Fedora/15/html/ > Musicians_Guide/sect-Musicians_Guide-CCRMA_Security_and_Stability.html > > > > I am not a systems programmer so I can't speak to these concerns. > > Some of the names of the real time kernel developers listed on the > > PlanetCCRMA kernel-rt page are Red Hat employees. > > > > I would like to see Fedora be the premier linux distribution for > > music. But until we can overcome the concerns listed in the > > Musician's Guide we will probably not have a real time kernel in the > > Fedora repositories. Maybe a Fedora "Re-Mix", or Fedora.Next and > > Workstation with the works with Fedora software library may break > > the ice. > > > > Well, I think those concerns are why Ubuntu moved to their low-latency > > kernel instead of their kernel-rt. According to their documentation > > (wiki) the lowlatency kernel is a "soft" preempt kernel and the rt > > kernel is "hard' but there's no docs on what make them different, and > > people in channel don't seem to know. > > (sorry for the very late response to this thread - busy busy busy, I > think it is still worth to comment on this) > > Brian, there is no "hard realtime" kernel for Linux. There are only > degrees of latency you can achieve with different combinations of > compile-time options, patching and runtime optimization. All of them are > "soft". You cannot guarantee deadlines on Linux - but you can get pretty > close with a fully optimized system and the RT patch, and if you have > the right hardware. > > I don't know what options Ubunutu uses to build their "low latency" > kernel, I imagine they just enable full preemption and irq threading. > This gives you better latency than a "non-preempt" kernel, but in my > experience that is not enough for realtime audio work with small buffers > (by that I mean jack running at 128x2 or 64x2). YMMV. > > To get really low latencies you need the RT patch (which has stability > issues as has been mentioned in the thread - there are as many testers > as for mainline). To fix those we would need more testers and proper bug > reports that are followed up. But of course that needs kernel gurus that > can respond. > > If you read this article you will see that the future of the RT patch is > not good at this point: > > http://lwn.net/Articles/617140/ > > Let's hope this gets better (it is not the first time that the rt patch > has lagged way behind mainline, I think a major rewrite happened in the > Fedora 1 or 2 timeframe and for a while there was nothing new). And BTW, > this is why we are currently stuck at 3.14.x in the Planet CCRMA > kernels, there is nothing newer... > > Sigh... > -- Fernando > >
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