My first brush with the new scheduler was when I came across http://lwn.net/Articles/350820/ via a mail to the LMMS lists (might have been LAU/LAD, can’t recall and lazy to search the archives or GMail trash). This prompted me to investigate it further, but not before I assumed some horrible things (mainly how the rt patch and the resulting realtime actually works). Suspecting my own judgement, I went over to #ck (irc.oftc.net) and posted my queries. True enough, part of my thinking was right – in that BFS can be a drop-in replacement for realtime audio work (traditionally so used to the -rt patch).
First of all, the “realtime” we have access to in an rt-patched kernel is “hard real, realtime”. Now, do recall that this patch was never designed with multimedia usage at the top of the priority list, but that it simply became a by-product of sorts. Primarily, we’re talking “embedded” and “lasers” here, then “audio”. Before this, us audio users only had this patch as our sole saviour. Well, not anymore.
Reason 1: The rt-tree has been slowly merged in mainline. Well, to an extent at least. As such, people have claimed to be able to run shitloads of VSTs and jconv IRs while recording a guitar sitting on top of Mt. Everest without -rt. The simple answer here is that “we no longer need a patch”.
Reason 2: Due to the revelation of BFS, users have found out that the “desktop experience” can apparently be better by a significant leap. Indirectly, this also means multimedia realtime becomes better proportionately. And this is not something hypothetical, you would (not should) immediately notice the difference if you’re a regular Linux Audio guy. What BFS introduces is a better “soft realtime” via SCHED_ISO, and this is more than enough unless we are audio rocket/laser scientists. Furthermore, in the BFS FAQ, Con Kolivas mentions realtime and jackd.
An extract of the conversation (by reading the following you agree not to hold anyone responsible for their comments and that it is just for your information):
[23:03] <Diablo-D3> bfs has realtime-compatible latencies
[23:03] <Diablo-D3> iso’ed processes on bfs generally defeats the entire point of having rt
[23:03] <mb_> Diablo-D3: It doesn’t change interrupt and spinlock latencies.
[23:03] <Diablo-D3> no it doesnt
[23:03] <Diablo-D3> but for something like, say, daft punk discovering linux, its good enough
[23:04] <Diablo-D3> if I was building a cruise missile, I wouldnt be using linux to begin with.