[NTLUG:Discuss] Re: pci-e and linux ( and radeon -vs- nvidia )

[Justin M. Forbes]

On Wed, Dec 22, 2004 at 07:25:20AM -0800, Bryan J. Smith wrote:
> On Wed, 2004-12-22 at 06:20, Jack Snodgrass wrote:
> 
> Any reason you wouldn't consider AMD?  As I noted in my other post, the
> nForce4 is now shipping in a couple of mainboards.
> 
AMD makes a great Linux box, and most of my systems are AMD64 based, though
I do have an intel em64t box, which is not bad... I would not pick up an
NForce 4 board yet for Linux.  I am not saying it will not work, just
saying that those of us actually working on the Linux implementation on
AMD64 have not seen it yet, so there are parts which *might* not work. 

> 
> >From what I've seen -- just like SATA is to ATA, PCIe is to PCI --  it's
> a serial channel that appears as a logical parallel implementation of
> the same.  So PCIe channels just look like bridged PCI busses.  Don't
> quote me on this, but the support is clearly there.
> 
This is not entirely accurate, and SATA is a really bad example here. It
changed enough that from a kernel standpoint, it is based on the SCSI
subsystem, not the IDE.
PCI-Express has some significant differences, but it is now well supported
in the kernel.
> 
> [ Unfortunately, it doesn't appear that the nVidia GeForce 6200 is
> officially supported with the latest 1.0-6629 drivers, yet. ]
> 
But everything else they are shipping right now is supported.

> 
> ATI is working hard to "catch up" right now.  They should be commended
> for their past XFree/Xorg efforts, but reality finally "sunk in."  I
> don't know how extensive the card support is yet, but it's not the
> entire line.  And they do _not_ support Linux/x86-64 yet.
> 
ATI is making an effort, but much of their linux work was done by non ATI
employees (whereas nvidia employees even maintain their 2D nv driver in
xorg).  The 8500 series 3D drivers were done by consultants.  Their drivers
have been somewhat spotty, and will continue in that direction for the
forseeable future.

> includes both AGP and PCIe.  In fact, since AGP is an "Intel trade
> secret" whereas PCIe is a "PCI Standards Group" standard, PCIe is
> actually "more open."  E.g., No more AGPgart crap -- the Linux kernel
> implementations _suck_, and for AGP cards, I _always_ used nVidia's
> driver integrated support instead.
> 
Actually, the AGPGart code is not too bad on some chipsets, the problem is
the implementation varies considerably.  If you are using an nForce 2
chipset, you really should use the nvidia graphics cards/drivers.  Outside
of that Dave does a pretty good job with agpgart considering the miniscule
amount of vendor suppore there.

> series.  And since nVidia's current "AGP cash cows" are the GeForce
> FX5200, FX5500 and FX5700"LE, they won't release an AGP version of the
> 6200.
> 
To do so, they would have to use the PCI-Express to AGP bridge chip, they
did this in the 6600 series for AGP, and performance on it is good, but
that is an extra chip, and eats into margins.  Much harder to swallow at
that price point.

> But be _wary_ of the new, _cheaper_ GeForce 6200 with "TurboCache." 
> What is it?  It's a card that has only 16MB, 32MB or 64MB of _local_
> SDRAM.  It uses the increased DTR/priority of the PCIe channels to use
> main memory for additional buffer/texturing.  It's cheaper, but for
> gamers, it's not worth the $10-40 savings over a _true_ 128MB 6200 card.
> 
I fear the driver implementation to support that.  Linux users would be
well advised to stay far away from a 6200 Turbocache.
> 
> P.S.  Again, I haven't checked to see if/how SLI works under Linux with
> GLX, if at all.  SLI is different this time around, but with GLX, I
> think it will be supported because it's easier to do than with DirectX
> (which is not so tight on specifications).  But that's just assumptions.
> 
It will be supported at some point, nvidia uses a similar code base for
their windows and linux drivers.  Generally, SLI is not ready for prime
time yet though, if you are willing to put up with instability for a
performance boost in a specific game, it might be worth it. 

Justin