>
> Kind Regards
>
> /Lars
>
> 2009/2/2 Robin Gareus :
> > -----BEGIN PGP SIGNED MESSAGE-----
> > Hash: SHA1
> >
> > krgn wrote:
> >> On Sun, Feb 1, 2009 at 3:08 AM, wrote:
> >>
> >>> On Sun, 01 Feb 2009 04:42:40 +0100
> >>> Robin Gareus wrote:
> >>>
> >>>> -----BEGIN PGP SIGNED MESSAGE-----
> >>>> Hash: SHA1
> >>>>
> >>>> Fernando Lopez-Lezcano wrote:
> >>>>> On Fri, 2009-01-30 at 03:23 +0100,
torbenh@gmx.de wrote:
> >>>>>> On Thu, Jan 29, 2009 at 03:41:48PM -0800, Fernando Lopez-Lezcano
> >>>>>> wrote:
> >>>>>>> On Tue, 209-01-27 at 14:06 +0100, Peder Hedlund wrote:
> >>>>>>>> Quoting Ken Restivo :
> >>>>>>>>
> >>>>>>>>> And here is the next installment in the saga of trying to get
> >>>>>>>>> Ingo RT going on my Asus EEE.
> >>>>>>>>>
> >>>>>>>>> I successfully built and ran the 2.6.26.8-rt12 with the
> >>>>>>>>> alsa_seq patch. It ran.
> >>>>>>>>>
> >>>>>>>>> The problem is that neither the Ethernet (atl1e) or wireless
> >>>>>>>>> (rt2860sta) work. So I pretty much had to reboot back out of
> >>>>>>>>> it immediately.
> >>>>>>>> I've been running the standard kernel from openSUSE 11.0 on my
> >>>>>>>> Athlon 2000+ and can get down to at least 5.3ms latency on an
> >>>>>>>> Audiophile 2496 using the limits.conf "trick".
> >>>>>>>>
> >>>>>>>> Do people really need lower latencies for music purposes or are
> >>>>>>>> we just thinking "well, I needed the RT patch three years ago; I
> >>>>>>>> ain't stopping now" ?
> >>>>>>> It depends on your usage (this question seems to come up every
> >>>>>>> couple of months lately). The current kernels are much better in
> >>>>>>> low latency applications than three years ago. They are usable if
> >>>>>>> you don't require "low" latencies (64 or 128 x 2). What you get
> >>>>>>> also strongly depends on the hardware mix you have.
> >>>>>>>
> >>>>>>> If you want to use 64 or 128 frame periods (or less) you probably
> >>>>>>> will need at rt patched kernel in most cases. Then again if an
> >>>>>>> occasional xrun is not a problem then you would be fine with the
> >>>>>>> stock kernel.
> >>>>>> i am running with -p64 -n3 on an intel-hda with 2.6.28
> >>>>>> of course internal cards have the greatest potential for
> >>>>>> lowlatencies. so this might be unfair, compared to pci.
> >>>>> Hmmm, I'm not sure, the load on pci itself by a soundcard should be
> >>>>> nothing really hard. What would the internal card use? Would not
> >>>>> that be pci or pci express anyway?
> >>>>>
> >>>> surely they are.
> >>>>
> >>>> $ lspci | grep Audio
> >>>> 00:1b.0 Audio device: Intel Corporation 82801G (ICH7 Family) High
> >>>> Definition Audio Controller (rev 02)
> >>>>
> >>>> The RT patch does two things:
> >>>> It allows to prioritize interrupts and it [almost] guarantees
> >>>> real-time scheduling for a dedicated process or thread.
> >>>>
> >>>> While the soundcard is low bandwith on the PCI bus, IRQ prio may still
> >>>> be required to override HDD and [sometimes] graphics I/O; at least
> >>>> when playing or recording many tracks. NTL, you can get a perfect
> >>>> x-run free system without the RT patch; you can just not rely on it
> >>>> to be as x-run free as a RT patched kernel ;)
> >>>>
> >>>>>> and i havent really seen xruns which i could not relate to some
> >>>>>> programm which wasnt RT-safe, and i am compiling stuff most of the
> >>>>>> day... though perhaps i am not pushing the DSP load hard enough.
> >>>>>>
> >>>>>> i did not even turn preemptible RCU on.
> >>>>>> the latency measurement instrumentation is also in 2.6.28 btw.
> >>>>> Well, that's very good news then!
> >>>>>
> >>>>> I think the last time I tried to use a non-preempt was 2.6.27.x
> >>>>> (maybe, I would have to double check). Playing 24 channels in
> >>>>> ardour would result in xruns, not very often but they would happen,
> >>>>> this is with 128x2 on an RME hdsp card runing on a quad core intel
> >>>>> system. I should try again with the latest available.
> >>>> I just booted into a vanilla 2.6.28.2 #1 SMP PREEMPT
> >>>>
> >>>> right, there's no realtime patch, yet running jackd at 64 * 3 @48kSPS
> >>>> on a HDA - ardour2 with 12 tracks, a couple of LADSPA effects and
> >>>> jamin (lots of CPU!) - there's no xruns yet!
> >>>>
> >>>> I'll be back in the studio in two weeks from now to test it with USB
> >>>> and 1394 devices. With <=2.6.24 kernels those were always working more
> >>>> reliably that the HDA so I don't expect problems there.
> >>>>
> >>>> BTW. with 2.6.28 I needed to
> >>>>
> >>>> `echo -1 > /proc/sys/kernel/sched_rt_runtime_us`
> >>>>
> >>>> or edit /etc/sysctl.conf and add
> >>>> sys.kernel.sched_rt_runtime_us = -1
> >>>>
> >>>> before JACK was able to acquire real-time privileges.
> >>> May I ask what that does? This value is 950000 on my system.
> >>> I think jack has rt privileges here on 2.6.28.2 but I'm not too certain.
> >>> I don't even know how to check that reliably.
> >>>
> >>
> >> jackd would not start with -R if realtime permission can not be granted. I
> >> think you would know if there was a problem ;)
> >> I have to say I don't know either what this option is you are setting,
> >> Robin. Is that the granularity of the timer (in u-sec's)? Setting to -1
> >> seems to suggest that the highest possible value is used, although I'm only
> >> wildly guessing. Would be great to know!
> >
> > indeed, jackd did not start unless run as root or until I changed
> > /proc/sys/kernel/sched_rt_runtime_us
> >
> > It's the us (or .001% of CPU usage?!) above which FIFO and RR will be
> > throttled to recover from a run-away rt process. - I'm not exactly sure
> > why it affects jackd when run as "normal" user; maybe because with CPU
> > load above the default 95% rt can not be guaranteed.
> >
> > There's a bit [off topic] but enlightening info at
> >
http://kerneltrap.org/mailarchive/linux-kernel/2008/8/16/2960524
> >
> > BTW. in sysctl.conf it's not "sys.kernel..." but
> > kernel.sched_rt_runtime_us = -1
> >
> > robin
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