[mythtv-users] ffmpeg and multiple CPUs. Was: Should I be switching to 0.21?

[W.Kenworthy]

On Mon, 2008-04-14 at 20:18 -0700, David Brodbeck wrote:
> lemongecko at gmail.com wrote:
> > Telling ffmpeg you have one CPU was the right choice. We do a lot of
> > FEA analysis at work, and we did plenty of benchmarking on HT CPUs
> > when they came out. We saw results similar to yours, though completely
> > disabling HT in the BIOS *improved* our performance.
> >   
> That's been my experience as well.  In one case I had a system that was 
> acting as a VPN gateway on a gigabit network.  Throughput went up 
> significantly when I turned HT off in the BIOS.  I also turn it off on  
> machines in our high-performance computing cluster.
> 
> The fact that more recent Intel CPUs don't seem to support this feature 
> makes me suspect it was something of a boondoggle all around.  Intel 
> seems to have given up on it and just moved to putting two or four whole 
> CPUs on one chip.
> 
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>From what I have read, its because there is a long and short processing
pipeline.  Linux is not that great in allocating the right processing to
the right pipeline so things block until the other thread has
progressed. This is particularly evident on database searches on HPC's.
Not sure if windows is any better at HT processing, but I have not seen
any figures.

I suspect its turn SMT/HT on for a desktop (good response, low load) and
off for high throughput applications like myth - or buy a real SMT MB :)

BillK