[mythtv-users] Standard PCI VDPAU-capable Video Cards vs. PCIExpress

[Brian Wood]

On Sunday, November 28, 2010 10:01:27 am Josh Mastronarde wrote:

> 
> Speaking as someone who worked on PCI and PCIExpress chipsets for a
> major chip manufacturer (but who is prone to getting the calculations
> wrong, so check them!):
> 
> Standard PCI runs at 33MHz x 32 bits (4 Bytes), for a max theoretical
> bandwidth of 133MB/s -- but because the same channel is used for
> commands and data in both directions, actual bandwidth will be much
> lower.
> 
> When used to transfer compressed data to a VDPAU card, 133MB/s =
> 1Gbit/s, which should be more than enough for any content.  20Mb/s HD
> content, for example, will only use ~2% of the max bandwidth, so
> there shouldn't be any impact on other system uses (and in most
> current systems, the expansion PCI slots are on a dedicated bus, so
> you're not sharing that 133MB/s with as many of the system
> controllers as originally).  CPU throttling shouldn't affect this,
> and I'd expect (without doing any calculations) that there's enough
> bandwidth for OSD drawing, etc.
> 
> However, when not using VDPAU and decoding in software to the frame
> buffer, that same HD content takes 1920x1080x4 Bytes/pixel =
> ~8MB/frame, at 60fps = 486MB/, which is way beyond the PCI
> capabilities.  So you're pretty much committed to VDPAU, whereas with
> PCIExpress you'd be able to use software decode for any codecs that
> the hardware can't handle.  I don't use VDPAU today, so don't know
> how much of a risk this is.

Thanks, that confirms what I suspected, anything that VDPAU can't deal 
with would be a potential problem. Even the OSDs might become a problem, 
similar to the problems with XVmC showing monochrome OSDs in the "bad 
old days".

> 
> I can't comment on Socket 939 itself, but as it's our competitor's
> product I'm obligated to say that there are better solutions out
> there

I agree, but those "better solutions" are not sitting in my garage at 
the moment :-). For what I want the 939s are "good enough".

I'm using Opteron 165s (Denmark Cores), which overclock seemingly 
without limit (or rather, it's the mobo that's limiting things). The 
CPUs will clock as fast as any mobo I own will handle, without even 
having to bump the core voltage. They outperform my FX60s, and certainly 
cost a lot less when new. I'm using DDR2 RAM that's certified by Kingston 
to O/C to 1066 (and does). The results are quite satisfactory, at least 
to me.

Thanks again.