Messages in this thread | | | Subject | Re: Latency results with 2.6.10 - looks good | From | Lee Revell <> | Date | Fri, 31 Dec 2004 22:18:44 -0500 |
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On Wed, 2004-12-29 at 14:33 -0500, Lee Revell wrote: > After testing JACK with vanilla 2.6.10, it appears that the scheduling > latency of 2.6.10 is a vast improvement over previous kernel releases. > JACK seems to be usable with a period of 32 and 64 frames, I cannot > produce xruns by moving the mouse or any amount of display or disk > activity. Previous kernel releases were somewhat worse than Windows XP > in this area, 2.6.10 is definitely better, maybe as good as OSX.
Followup: other audio users have confirmed that 2.6.10 is the best release yet latency-wise. It works most of the time at 64 frames (~1.33ms latency).
Now, the bad news: there are still enough xruns to make it not quite good enough for, say, a recording studio; as we all know with realtime constraints the worst case scenario is important. As expected the RT kernel beats it by a wide margin. I have attached some numbers, excerpted from a post by Rui on the JACK list. The JACK test used was described previously on this list.
Ingo, what are your plans for pushing more of the RT patch set upstream? It seems that the soft/hardirq threading and voluntary preemption (turning the might_sleep checks into preemption points) are required to further improve the latency of the standard kernel. These are well tested at this point and also zero cost for users who don't enable them. I think if these features go upstream before 2.6.11 then we can say all of the issues Paul raised, in that post months ago that led to the VP patches, will be put to rest.
We are finally within sight of Linux being the best multimedia OS available, out of the box - a position we had briefly in the 2.4 days, albeit with the low latency patches, and subsequently lost to OSX (IMHO). This is a milestone, everyone should be proud of this release.
Anyway, happy new year to everyone.
Lee
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Rui:
Now, let's get to the point. With the default workload (20 clients * 4 * 4 ports) I've ran it against a Con Kolivas' 2.6.10-cko1 patched kernel and the real jewel as is latest 2.6.10-rc3-mm1-RT-V0.7.33-04, which is Ingo Molnar's full PREEMPT_RT patched kernel. The tests were conducted on my P4@2.5G laptop, against the on-board alsa driver (snd-ali5451).
The jackd command line is therefore:
jackd -v -R -P60 -dalsa -dhw:0 -r44100 -p64 -n2 -S -P
The results speak for themselves :)
2.6.10-cko1 RT-V0.7.33-04 ------------- ------------- Timeout Rate . . . . . . . . : ( 0.0) ( 0.0) /hour XRUN Rate . . . . . . . . . . : 216.8 2.2 /hour Delay Rate (>spare time) . . : 395.2 0.0 /hour Delay Rate (>1000 usecs) . . : 375.8 0.0 /hour Delay Maximum . . . . . . . . : 4320 308 usecs Cycle Maximum . . . . . . . . : 845 1051 usecs Average DSP Load. . . . . . . : 44.0 50.2 % Average CPU System Load . . . : 14.4 31.7 % Average CPU User Load . . . . : 19.8 21.4 % Average CPU Nice Load . . . . : 0.0 0.0 % Average CPU I/O Wait Load . . : 0.1 0.1 % Average CPU IRQ Load . . . . : 0.0 0.0 % Average CPU Soft-IRQ Load . . : 0.0 0.0 % Average Interrupt Rate . . . : 1691.7 1692.6 /sec Average Context-Switch Rate . : 13368.8 18213.9 /sec
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