[LAU] Can't use HPET by JACK2 under kxstudio (probably, it is ubuntu problem too).

[Mike Cookson]

Thanks for reply. I tried again with generic, lowlatency and again - realtime kernels. It seems, problem for jack is caused by utility jack2-simple-config, shiped in kxstudio. There is forced restart function, which stupidly kills all daemons without any checks and preparation (though it warns, what will happen, proposing to wait :). It seems, when jackdbus is killed, hpet, probably, is not freed. Also when jack is started, 'lsof | grep hpet' gives two jackdbus-related items. And if i try to start yoshimi or patchage (using libjack, not dbus), they both try to use hpet... and fail :] . And also, runing jack (i used ladish, because ladiconf has clock source option), in gladish i noticed, that dsp load is equalk to some max... gladish showes dsp load in format <lower value> (<high value (usually - up to 100%)>) e.g., 1.5% (100%); with HPET clock first value was always same as second (growed from 75% up to 100%).

I added clocksource option to bootloader. Not sure yet, are there any changes (too hard to check for me).

Tue, 08 Mar 2011 07:59:53 +0000 письмо от Peter Nelson <peter at fuzzle.org>:

> On Tue, 2011-03-08 at 09:57 +0300, Mike Cookson wrote:
> > On attempt to use device (or even just try 'cat /dev/hpet'), it
> is
> > said, that device is busy. But jack has such option :/
> > I'm using kernel 2.6.33-rt. I can guess, that under rt kernel i
> should
> > not use HPET directly, because it is used by system,
> > and so, may be referred via 'system'. But even if that, such way
> could
> > bring some violations comparing to direct HPET usage.
> > 
> > May be indeed, HPET should be used directly only on non-rt systems?..
> > 
> > Btw, how i specified it: i have jack2 and ladish. Clock is specified
> > via ladiconf. Clock parameter type is integer; yesterday nedko showed
> > me a patch for jack, fixing this problem, where i saw order of
> > variants in enumeration (hpet variant is '2').
> 
> Jack's HPET support has an issue: /dev/hpet can only be opened a limited
> number of times. When you use -c hpet, as well as Jack itself, each
> client has /dev/hpet opened twice; once as an fd, and once as mmap. On
> my systems /dev/hpet is limited to 3 or 4 opens, so this is practically
> unusable for any Jack setup.
> 
> However you can tell the kernel to use HPET itself for the system clock:
> 
> echo hpet >
> /sys/devices/system/clocksource/clocksource0/current_clocksource
> 
> or put "clocksource=hpet" in your boot up command line.
> 
> And then -c system will use HPET, indirectly.
> 
> Peter.
> 
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