[mythtv-users] ffmpeg and multiple CPUs. Was: Should I be switching to 0.21?
John Drescher
drescherjm at gmail.com
Mon Apr 14 20:21:52 UTC 2008
On Mon, Apr 14, 2008 at 4:01 PM, Tom Dexter <digitalaudiorock at gmail.com> wrote:
>
> On Mon, Apr 14, 2008 at 1:42 PM, John Drescher <drescherjm at gmail.com> wrote:
> > > > However...and this is the interesting part...if I use ffmpeg but
> > > > switch the number of CPUs to 1 instead of 2 the performance of the two
> > > > is virtually identical. It seems that, at least with my
> > > > hyper-threaded 3 Ghz P4, ffmpeg works much better with a single core.
> > > >
> > You do realize hyperthereading can have a negative impact on
> > performance? I mean a single core P4 with hyperthreading may look like
> > two cores but it certianly is not. Hyperthreading works only because
> > the P4 had such a long pipeline that stalls occurred so frequently
> > (mispredicted branch ...) and in this case a second thread could be
> > executed where no ops would be inserted in the pipeline.
> >
> > John
> >
> >
>
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> >
>
> Yes I'm aware of that. When I first set up my frontend I tested both
> ways and the performance is better with it enabled.
>
> I just gave it another try and it still seems to be an improvement
> having it enabled.
>
I would like to make 1 point though, any improvement will will be
application and data specific. So having HT enabled may increase
performance by 20% in some application and decrease it by 5% in a
second application. In general it will increase performance though.
John
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