[linux-audio-dev] Jack and NPTL (again?)

Jonathan Woithe jwoithe at physics.adelaide.edu.au
Tue Nov 22 06:37:21 UTC 2005

Hi everyone

I've recently moved a system over to Slackware 10.2 which utilises NPTL and
I'm aware of the issues NPTL has raised in the past.  Based on a comment on
the Jack website though I sort of assumed that things were now in hand and
that Jack had a workaround in place for the issue.

Despite this I have found that jackd itself (when run using set_rtlimits)
gives an error (-11, EAGAIN) when "creating realtime thread".  I have
already confirmed that set_rtlimits does operate correctly in the NPTL
environment; it appears that for some reason pthread_create flatly refuses
to create the RT thread even though the appropriate priority limits are set
for the process.

The LD_ASSUME_KERNEL hack does make jackd work; however, it would be nice
to know what's going on (or whether in fact the problems are still being
worked on).  Are there any ideas?

Interestingly enough, jack applications (ardour for example) do NOT need
the LD_ASSUME_KERNEL hack - they start and operate fine without out.  Only
jack itself appears to have issues.

Glibc is 2.3.5, getconf reports "NPTL 2.3.5" and kernel is 2.6.14 plus
2.6.14-rt13.  2.6.14-rc3-rt4 has the same issues.  Oddly enough, it appears
that under 2.6.13 things work fine even for jackd, but I need to confirm
that tonight.  Jack command line (from memory):

  jackd -R -d alsa -d hw:0 -n 4 -p 512

Jackd compiled against 2.6.14 headers with gcc 3.3.6.  Kernel compiled with 
3.3.6 also.


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