[mythtv-users] S-video/nvidia problems

Brian Wood beww at beww.org
Fri Jul 30 16:19:30 UTC 2010

On Friday, July 30, 2010 09:46:23 am Eric Sharkey wrote:
> On Fri, Jul 30, 2010 at 11:27 AM, Brian Wood <beww at beww.org> wrote:
> > On Friday, July 30, 2010 09:07:28 am bhaskins wrote:
> >> IMHO YMMV shared memory is a nasty performance hit.
> >> I have added video cards to several systems and the users have often
> >> said it was like
> >> getting a new box.
> > 
> > Do you think this is due to RAM being taken away from the system, IOW, if
> > you add extra RAM to make up for what the video system is using would it
> > be the same as if you were using a discreet card?
> > 
> > Or is it due to the video system not performing as well with shared RAM,
> > as with a card, perhaps due to the RAM on the card being faster than the
> > system RAM?
> As far as I understand it, the bottleneck is the bus that connects the
> RAM to the rest of the system.  When video ram is shared with system
> ram, both the CPU and the GPU compete for time to do reads and writes
> to RAM on the same bus.  When the GPU has its own RAM, that contention
> goes away.
> Because of that, you can't improve the situation just by adding more
> ram, you need to add another bus, which isn't possible.

That's what I figured, thanks for the confirmation.

So using integrated video slows the entire system down, as well as not giving the same graphics performance.  I guess the 
only time integrated graphics makes sense is if the size/weight/heat/power/cost savings are worth the performance hit to 
you. If the result is "good enough" for you then it makes sense.

Even if you have no need for high-performance video (say an office environment), it still might pay to have a discreet video 
card, which would give you the effect of a CPU upgrade.

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