Re: [LAT] [LAU] Are RT-patches needed anymore? (Was Re: >= 2.6.27 RT ETA?)

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Fernando Lopez-Lezcano wrote: > On Fri, 2009-01-30 at 03:23 +0100, torbenh(a)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 &lt;ken(a)restivo.org&gt;rg>: >>>> >>>>> 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.