Re: [Jack-Devel] Can't bring F/P below 128

On 12/18/2011 10:12 PM, Ralf Madorf wrote:
> On Sun, 2011-12-18 at 20:51 +0200, Nikos Chantziaras wrote:
>> I'm stuck at 128 with a 5.33ms latency
>> In case it matters, I'm using kernel 3.1.5.
>
> A little bit OT, since I don't know how to find out what's going wrong,
> anyway, this might help:
>
> Since I can't see a rt patch for this kernel at
> http://kernel.org/pub/linux/kernel/projects/rt/.

I'm using BFS, not rt.  (AFAIK, rt is not really for audio.)  Using a 
vanilla kernel without BFS, 64 F/P with the Soundblaster give too many 
XRUNs.


> Do you use full preempt
> with threadirqs set?

I use full preempt and a 1000Hz tick.  But I don't know about 
threadirqs.  I've found lots of info on Google about the "threaded IRQ 
handlers", but none of them tell me how to enable this.  There's no 
option for that in the kernel config.  Searching for "thread" in 
menuconfig finds this:

   Symbol: IRQ_FORCED_THREADING [=y]│
   │ Type  : boolean│
   │   Selected by: X86 [=y]

But as you can see, it doesn't say where it can be enabled.  Maybe it's 
only for x86?  I'm on a 64-bit kernel.


> IMO even 10 ms fixed latency are ok, anyway, if you
> like to have less latency, you could try a kernel-rt

I tried an rt kernel in the past.  It behaved exactly like BFS 
latency-wise (maybe a bit worse even, when I have many applications 
running in the background,) except it had other negative effects on 
other software (performance seemed to go down a bit instead of 
improving.)  So for me, and on this system, BFS works best for both 
latency as well as multitasking performance/responsiveness.

I need to find out how to enable threaded IRQs and test again with that 
setting enabled.

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