Messages in this thread |  | | Date | Sat, 22 Sep 2001 20:18:43 -0700 | From | george anzinger <> | Subject | Re: [PATCH] Preemption Latency Measurement Tool |
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Andre Pang wrote: > > 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).
The one thing the latancytimes patch doesn't monitor is interrupt off time. Maybe it should...
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