18 Dec
2009
18 Dec
'09
1:38 a.m.
quick question:
if you are using jack with a vanilla kernel, should you still keep the
realtime option enabled in jack, or run jack without the -R? my
reasoning tells me that no realtime patch = no realtime in jack, but I
just wanted to check myself with you all...
--
Josh Lawrence
http://www.hardbop200.com
18 Dec
18 Dec
1:53 a.m.
Josh Lawrence wrote:
quick question:
if you are using jack with a vanilla kernel, should you still keep the
realtime option enabled in jack, or run jack without the -R? my
reasoning tells me that no realtime patch = no realtime in jack, but I
just wanted to check myself with you all...
Hi Josh,
Scheduling JACK to run with realtime priority (using the -R option) is
separate to having a kernel that runs with hard realtime pre-emption
enabled. Ideally, you want both, but on a vanilla kernel, you still want
the -R option -- indeed, that's how I run my systems.
One way to think of it is that running with realtime priority (with the
-R option) instructs the kernel to run JACK with the best scheduling it
can possibly manage. If you also have realtime pre-emption in your
kernel, though, then the kernel's best effort will be... well, better :)
Thanks
Leigh
2:25 a.m.
Josh Lawrence wrote:
quick question:
if you are using jack with a vanilla kernel, should you still keep the
realtime option enabled in jack, or run jack without the -R? my
reasoning tells me that no realtime patch = no realtime in jack, but I
just wanted to check myself with you all...
Have a look at the SCHED_FIFO section in 'man sched_setscheduler'
<http://linux.die.net/man/2/sched_setscheduler>
The 'realtime' jack option relates to the use of SCHED_FIFO (ie the
scheduling priority) on selected jack threads (but not all!). The
'realtime' kernel patch relates to different issues, eg, allowing user
processes to preempt kernel processing when possible && appropriate,
thus reducing inherent processing latencies. So the jack -R option is
desirable regardless of which kernel you're running. That's hardly a
complete description of the matter, but I think it's close enough for
now :-).
cheers, Cal
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Leigh Dyer