[linux-audio-dev] latency and P4 hyperthreading?

Steve Harris S.W.Harris at ecs.soton.ac.uk
Wed Jun 4 04:54:01 UTC 2003

On Tue, Jun 03, 2003 at 06:58:03 -0700, Fernando Pablo Lopez-Lezcano wrote:
> > > The problem is not speed but latency glitches. It certainly should be
> > > slower than a "real" dual cpu system but it could be slightly faster
> > > than the same uniprocessor machine with ht turned off. Of course if you
> > > have latency problems it is not very useful. 
> > 
> > I think its a better win if the kernel understands HT, 
> I thought it did, obviously it does not (completely). 

Some do, some dont. I'm not sure where the cutoff comes or if its a patch.
> > I have a smp ht
> > machine and big parallel therads sometime get stuck on different threads of
> > the same cpu, instead of different cpus. If I had no HT in those cases it
> > would be faster.
> Ha! So I was not imagining things. I had some weird problems when trying
> to run jack (but I was distracted with the latency issues so I did not
> pay much attention - one problem at a time) so most probably that is the
> reason. 

I dont knwo what (linux) thread affinity is like, it could be that if oyu
restart jack it will get its threads stuck to real cpus. If your on a UP
system it doesn't matter ofcourse, its only a problem where you have an
SMP system and all the virtual CPUs are not equal.

- Steve

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