pbd@Op.Net (Paul Barton-Davis) wrote on 02.07.00 in <200007030027.UAA02936@renoir.op.net>:
> I don't know whether they have gotten worse or better. It wouldn't
> suprise me if they've never been that good. Linus says that latency
> has always been a concern of his, and its possible that for the main
> kernel code, this is reflected, but that various device drivers and
> changes to them over time don't show the same care. Its also possible
> (i might even guess likely) that most kernel developers rarely if ever
> run applications that require this kind of behaviour, and so the
> kernel has possibly never had much better performance than it does
> now.
I think it's not so much that people don't care, as that until recently,
people didn't have a good way to measure the latency.
I certainly do remember the recurring debate about "interactive
responsiveness", which is *exactly* the kind of latency we are talking
about here - in this case, from pressing a key (thus generating an
interrupt) to seeing the echo from, say, vi (thus getting a process to
run).
But I also recall that the comments were "this feels much snappier", "this
feels like molasses". You just can't optimize for 5ms latencies on the
basis of feelings. Humans are bad at doing this kind of measurements.
MfG Kai
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