[linux-audio-dev] XAP spec & PTAF comments [merge]

Steve Harris S.W.Harris at ecs.soton.ac.uk
Sun Feb 9 08:37:01 UTC 2003


On Sun, Feb 09, 2003 at 11:13:53 +0100, David Olofson wrote:
> On Sunday 09 February 2003 01.18, Steve Harris wrote:
> [...silence and RT...]
> > I suspect (but have no intention of finding out) that suddenly
> > waking up a large subnet will have large chace effects too, so it
> > wont be a case of just the CPU load varying.
> 
> I suspect that unless most of the memory used by each "mode" of the 
> net fits in the cache, the difference won't be all that big, since 
> every block cycle causes massive amounts of cache misses anyway. 
> Also, as soon as you have hand disk recording going on, you'll have a 
> butler thread throwing RT data out of the cache all the time. (Same 
> effect that has surprized some RTL and/or RTAI users by causing 
> *higher* latencies for the RT threads on faster CPUs.)

There is also the instruction cache to think of. Practical experience
suggests that suddenly waking up a chain of plugins causes a spike of CPU
load which settles down. It may be possible to moderate this with carefull
coding however.

- Steve



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