Messages in this thread | | | From | Benno Senoner <> | Subject | 2.4.0test5-pre4-lowlat latencies benchmarked, 2.2.16+Ingo's LL patch = strange behaviour | Date | Wed, 26 Jul 2000 00:41:33 +0200 |
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Hi,
here the tests of Andrew's lowlatency patch on 2.4.0-test5-pre4:
Unfortunately during disk writes it performs still quite bad , about 50msec during disk writes.
first test with CPU usage=80% , 2nd CPU usage=10% (cpu usage = latencytest which artificially wastes CPU in an empty loop)
http://www.gardena.net/benno/linux/audio/2.4.0test5-cpu80/3x256.html http://www.gardena.net/benno/linux/audio/2.4.0test5-cpu10/3x256.html
Although better than standard kernels we are still about 20times worse than Ingo's 2.2.10/2.2.15 patches, and speaking in other OSes terms still 5-7 times worse than Windows/MacOs. So far for the 2.4 kernels.
Additionally, I tested Redhat's kernel 2.2.16-3 + Ingo's 2.2.15 patch, and we made rpms and src.rpms available here: http://www.gardena.net/benno/linux/lowlatency-rpm.html
The very strange thing is that 2.2.16 although the latency behaviour is good it shows high spikes (around 2msec) at regular intervals, and you see that these are in green, which means that when our thread is in the cpu wasting loop, something pre-empts us and chews away about 2msec.
Notice the box is my reference machine which produced excellent behaviour with 2.2.10. I tested 2.2.15+lowlat (original 2.2.15 kernel, not Redhat's one) too and I do not see the green spikes. So it must be either something which happened during the 2.2.15 -> 2.2.16 transition , or the cause are the Redhat patches
http://www.gardena.net/benno/linux/audio/2.2.16cpu80/3x128.html http://www.gardena.net/benno/linux/audio/2.2.16cpu10/3x128.html
Ingo, Andrea any guess ?
I will retry with a fresh 2.2.16 to see if the problems go away.
BTW: there is now a version of latencytest available which outputs PNG instead of GIF, because some people reported that their libgd does not support GIF anymore. So if you have problems with the GIF version grab the PNG version here: http://www.gardena.net/benno/linux/latencytest-0.42-png.tar.gz
cheers, Benno.
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