Wed, 20 Sep 2000 [EMAIL PROTECTED] wrote:
[...]
> What I noticed during my tests is that sometimes my realtime tasks takes
> very different times to complete, with a minimum of about 110 microseconds
> and a maximum of about 350 microseconds.
[...]
Are you using FP or some more "advanced" math functions?
In the first case, there's a chance that what you're seeing is denormal number
slowdowns (a common problem when dealing with real time audio processing). It's
a result of extremely small numbers hitting FPU performance, since they're
special cases. (When the exponent underflows, the mantissas have to be
denormalized, and the implicit 1 bit above it has to be disregarded. BTW, this
applies to most FPUs, not only those of the x86 family.)
In the latter case, look for anything that uses code from some math lib, or
possibly your own code - there may be iterative operations that take longer
under certain circumstances.
A third possibility: It seems to me that it isn't X, but rather the
applications that affect you RT task. (Otherwise running X on NT - or any
other alternative to a local X server - probably wouldn't have the same effect
as running a local server. It *could* be the library and not the server,
but...) That is, it might be *any* form of system stress that affects the RT
task.
My guess would be that the fluctuations in execution time are the result of
cache misses caused by the applications flushing RT data out of the cache. The
Celeron has 128 kB of full core speed cache, and a 66 MHz system bus, so there
can be quite some difference between accessing hot and cold data. Are you using
lots of data, look-up tables or anything like that?
David Olofson
Programmer
Reologica Instruments AB
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