Messages in this thread | | | From | Benno Senoner <> | Subject | Re: Low-latency patches working GREAT (<2.9ms audio latency), see testresults ,but ISDN troubles | Date | Mon, 30 Aug 1999 01:41:58 +0200 |
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On Sun, 29 Aug 1999, Ingo Molnar wrote: > On Sat, 28 Aug 1999, Benno Senoner wrote: > > > - The disk performance decreases by 10-25% when I increase the CPU load > > in the "latencytest" bench. (On light CPU load there are no disk > > performance differences, maybe this is related to higher scheduling > > overhead) > > just in case anyone misunderstood the above result (as i think many did). > The 'CPU load' mentioned above is a _realtime process_ (unless Benno you > changed the benchmark). This is a _good_ result. 'increase CPU load' > simply means 'generate more RT load' - which in _this case_ might mean > less disk performance - but the RT task asked for it in the first place. > All in one: i can see no problem here.
Ingo, you are right: I just ran the unmodified latencytest and was measuring disk performace. In my example I used 1.45ms fragments, this means that my realtime thread has to be rescheduled about 600times/sec , and during each 1.45ms cycle the rt thread wastes about 1.1ms (= 80% of 1.45ms) of the CPU.
If you lower the CPU load to low values ( 10% for example) , there is not a big substantial disk WRITE performance loss compared to an unpatched kernel.
The interesting thing is that the disk READ performance is unaffected by your patches, on CPU loads of 80% I get the same disk READ performance on your lowlatency-N6 kernel as on a standard kernel. Perhaps the problem lies in your modifications in the disk write code ?
> > if a 'simple' CPU-user (non-RT) is getting more active there is no > slowdown.
I don't tested this yes, but I think you are right. (Will report back some numbers when I get the benchmarking done).
You said your patch was 100% stable: are we talking about the same patches ? The latest I got was -N6 + shm.c backed out + Roger's conditional_schedule() wrapping in filemap.c.
The kernel is rock solid , except it crashes when I do a modprobe of the ISDN hisax.o module.
regards, Benno.
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