Benno Senoner wrote:
>
> On Sat, 12 Aug 2000, Andrew Morton wrote:
>
> >
> > - Benno's `latencytest' tool is odd. It claims that it sees ~30
> > millisecond scheduling bumps. Same with Ingo's patch. It is not
> > obvious what is going on here. When his background workload is run
> > against `amlat' everything is fine.
>
> What does mean "odd" ?
> These 30msec are for REAL, believe me !
Yes, it's obvious that more work is needed here. We can't offer these
patches as "solutions" with outstanding mysteries like this.
I modified `amlat' so that after every SIGIO it chews 80% of an interrupt
interval. My approach was to just spin on the value of the TSC. According
to `ps' it is amazingly accurate. Could you please take a look and let me
know if you can spot anything which can explain this?
http://www.uow.edu.au/~andrewm/linux/amlat.tar.gz
> Andrew, if you think that my tool is flawed, then write a little app which
> opens the audio device with 3x256 buffers ( = 4.4msec buffersize),
> read a wav into mem, call mlockall() and then play simply from ram
> eg:
> ( buffer[] contains the wave (array of shorts))
> offset=0;
> while(1) {
> write(audio_fd, &buffer[offset], 256);
> offset += 256;
> }
>
> excatly when latencytest registers greater than 4.4msec peaks you will hear
> crackles, skips and pops.
OK, I'll take a look, work out what's going on.
-
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