Messages in this thread |  | | Date | Sat, 22 Sep 2001 17:22:21 +1000 | From | Andre Pang <> | Subject | Re: [PATCH] Preemption Latency Measurement Tool |
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On Sat, Sep 22, 2001 at 02:10:18AM -0400, Robert Love wrote:
> > i did a test of it on linux-2.4.10-pre13 with Benno Senoner's > > lowlatency program, which i hacked up a bit to output > > /proc/latencytimes after each of the graphs. test results are at > > > > http://www.algorithm.com.au/hacking/linux-lowlatency/2.4.10-pre13-pes/ > > > > and since i stared at the results in disbelief, i won't even try > > to guess what's going on :). maybe you can make some sense of > > it? > > Well, its not hard to decipher...and really, its actually fairly good. > the latency test program is giving you a max latency of around 12ms in > each test, which is OK.
arrgh! i just realised my script buggered up and was producing the same graph for all the results. please have a look at the page again, sorry.
apart from that, i'm still confused. compared to other graphs produced by the latencytest program, my system seems to have huge latencies. unless i'm reading it wrongly, the graph is saying that i'm getting latencies of up to 30ms, and a lot of overruns. compare this to
http://www.gardena.net/benno/linux/audio/2.4.0-test2/3x256.html
which shows latencytest on 2.4.0-test2, and
http://www.gardena.net/benno/linux/audio/2.2.10-p133-3x128/3x128.html
which are the results for latencytest on 2.2.10. admittedly these kernels are much older, but i'm consistently getting far more latency than those kernels. that's the bit i'm confused about :) i've tried Andrew Morton's low-latency patches as well, to no avail. i've made sure i've tuned my hard disks correctly, and i don't have any other realtime processes running.
am i concerned with a different issue than the one you're addressing?
> the preemption-test patch is showing _MAX_ latencies of 0.8ms through > 12ms. this is fine, too.
yep, i agree with that ... so why is latencytest showing scheduling latencies of > 30ms? i get the feeling i'm confusing two different issues here. from what i understand, /proc/latencytimes shows the how long it takes for various functions in the kernel to finish, and the latencytest result shows how long it takes for it to be re-scheduled (represented by the white line on the graph).
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