[mythtv-users] S-video/nvidia problems

Eric Sharkey eric at lisaneric.org
Fri Jul 30 15:46:23 UTC 2010


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.

Eric


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