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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