[linux-audio-dev] Re: Pragmatic comparison of approaches to audio engine

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Subject: [linux-audio-dev] Re: Pragmatic comparison of approaches to audio engine
From: Paul Davis (pbd_AT_Op.Net)
Date: Mon May 14 2001 - 13:54:07 EEST


>Ok, I've finished a new version of ctx.c that complete the picture
>adding multi process approach.

this looks pretty good. my only point of contention would be the
rather small memory footprint of the the process, which i'm not
totally sure is realistic for actual components in a system like
this. If you look at the numbers for lat_ctx, the cost of the
inter-process context switch rises fairly significantly as the
process' memory footprint increases.

>Results are *very* interesting.

I would be interested to see what you think of them.

To me, they still suggest that you the multiprocess approach is not
scalable for low latency real-time work. Clearly, as processor speed
increases, things only get better, though this may be reduced in a
noticeable way if the memory footprint expands. But your numbers
suggest that on an 800MHz machine, with 5 very, very small components
(nothing like xmms, terminatorX, ardour, spiral loops etc.) you'd
spend about 1.5% of the CPU time on switch overhead. On a 333MHz CPU,
that would be more like 10%.

It would be interesting to know the slope of the two curves: more
overhead as memory footprint goes up; less total time as processor
speed increases. Would you mind trying to measure the former, since
the latter is linear, more or less?

If the memory footprint doesn't have a dramatic effect, I'd be willing
to consider the multi-process model since processor speeds are already
in the 1.5GHz range. If it does, then I think that a single-threaded
design is the only option for a low-latency real-time situation.

--p


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