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Saphire 7950 PCIe Lanes

thedocbwarren

thedocbwarren

macrumors 6502
Original poster
Nov 10, 2017
430
378
San Francisco, CA
I have a Mac Pro 2010 (5,1) with an EFI Sapphire 7950 (boot screen) running. Everything seems great except I wondered why the system report shows the PCIe lane width as 4x. This machine has 2 16x slots for GPUs. I have it in the so label 16x slot. I have moved this card around to test with no change. I have no idea why this would restrict the bandwidth of the card unless it's a bug.

Machine running High Sierra.
 
thedocbwarren said:
I have a Mac Pro 2010 (5,1) with an EFI Sapphire 7950 (boot screen) running. Everything seems great except I wondered why the system report shows the PCIe lane width as 4x. This machine has 2 16x slots for GPUs. I have it in the so label 16x slot. I have moved this card around to test with no change. I have no idea why this would restrict the bandwidth of the card unless it's a bug.

Machine running High Sierra.
Click to expand...

Do you have any picture of your card?

Most 7950 has dual ROM design, switch to another ROM (most likely no boot screen, doesn't really matter), and then try again.

If other GPU can negotiate at x16, then obviously it's the GPU's problem, not the Mac Pro.

Anyway, no need to worry if you really can't fix it. The performance penalty is just about 2.4%, pretty much zero impact on most operation.

https://forums.macrumors.com/thread...mac-with-2-d700s.1732849/page-5#post-21722712
 
It’s that real pretty white card. It does have the dual firmware mode for PCs. It’s got s boot screen so it’s set for EFI. I will try another card for gits and shiggles. That said I did notice the geek bench compute is very good and FCPx runs very well so maybe it’s a “who cares.”

h9826790 said:
Do you have any picture of your card?

Most 7950 has dual ROM design, switch to another ROM (most likely no boot screen, doesn't really matter), and then try again.

If other GPU can negotiate at x16, then obviously it's the GPU's problem, not the Mac Pro.

Anyway, no need to worry if you really can't fix it. The performance penalty is just about 2.4%, pretty much zero impact on most operation.

https://forums.macrumors.com/thread...mac-with-2-d700s.1732849/page-5#post-21722712
Click to expand...
 
thedocbwarren said:
It’s that real pretty white card. It does have the dual firmware mode for PCs. It’s got s boot screen so it’s set for EFI. I will try another card for gits and shiggles. That said I did notice the geek bench compute is very good and FCPx runs very well so maybe it’s a “who cares.”
Click to expand...

If that's the genuine 7950 Mac Edition card. Then most likely it's damaged. From memory, it's possible that damage some transistor near the PCIe connector during installation / uninstallation, which makes the card can only negotiate at x4 lane.

If you buy it cheap, and the card is 100% stable, then I will say performance penalty is not a problem at all. But I guess if you pull the card out and examine the card's back carefully, you may able to find out the "why".
 
h9826790 said:
If that's the genuine 7950 Mac Edition card. Then most likely it's damaged. From memory, it's possible that damage some transistor near the PCIe connector during installation / uninstallation, which makes the card can only negotiate at x4 lane.

If you buy it cheap, and the card is 100% stable, then I will say performance penalty is not a problem at all. But I guess if you pull the card out and examine the card's back carefully, you may able to find out the "why".
Click to expand...
[doublepost=1510343361][/doublepost]Definitely not cheap and brand new. So curious. I’ll try the nvidia card for fun. I have faster machines I use anyway so it’s more for optimized FCPx usage. The nvidia cards work less optimized for it but well enough.
 
hwojtek said:
I'm not quite sure this is a right direction, but perhaps there is some insight here...?
Click to expand...

Wrong direction. The Sapphire HD7950 Mac Edition negotiate at PCIe 2.0 speed natively. No need any transistor mod. Also, that's nothing to do with x4 or x16.
[doublepost=1510352668][/doublepost]
thedocbwarren said:
[doublepost=1510343361][/doublepost]Definitely not cheap and brand new. So curious. I’ll try the nvidia card for fun. I have faster machines I use anyway so it’s more for optimized FCPx usage. The nvidia cards work less optimized for it but well enough.
Click to expand...

In this case, contact the seller. Get a replacement (or refund).

I don't think both of your cMP's PCIe slot 1 and 2 are broken. Of course, still better to try another card, just make sure something can run at x16. Or put this card in another machine to confirm it is a faulty card.

And yes, this card has exceptionally good performance in FCPX. But if you don't really need boot screen. And you can run 10.12.6 or higher. I think you better return the card, and get the Sapphire PULSE RX580 8GB card. That's cheaper than a brand new HD7950 Mac Edition card, newer, and much faster in all aspect (including in FCPX).

It is a 100% OOTB card, but just no boot screen.
 
Good call. I’ve been tempted to try a new AMD card. The 7950 is exceptional for sure but uses a lot of power and out of date. I use Nvidia GPUs for other purposes with success, however, no denying AMD is a finalcut performer.



h9826790 said:
Wrong direction. The Sapphire HD7950 Mac Edition negotiate at PCIe 2.0 speed natively. No need any transistor mod. Also, that's nothing to do with x4 or x16.
[doublepost=1510352668][/doublepost]

In this case, contact the seller. Get a replacement (or refund).

I don't think both of your cMP's PCIe slot 1 and 2 are broken. Of course, still better to try another card, just make sure something can run at x16. Or put this card in another machine to confirm it is a faulty card.

And yes, this card has exceptionally good performance in FCPX. But if you don't really need boot screen. And you can run 10.12.6 or higher. I think you better return the card, and get the Sapphire PULSE RX580 8GB card. That's cheaper than a brand new HD7950 Mac Edition card, newer, and much faster in all aspect (including in FCPX).

It is a 100% OOTB card, but just no boot screen.
Click to expand...
 
  • Chipset Model: AMD Radeon HD 7950
  • Type: GPU
  • Bus: PCIe
  • Slot: Slot-1
  • PCIe Lane Width: x16
  • VRAM (Total): 3072 MB
  • Vendor: ATI (0x1002)
  • Device ID: 0x679a
  • Revision ID: 0x0000
  • ROM Revision: 113-E2080C-101
  • EFI Driver Version: 01.00.624
 
That looks right, sadly mine doesn't. I guess it's ok for now but going to troubleshoot a bit more. Mine says 4x lane width.

Michael MP2 said:
  • Chipset Model: AMD Radeon HD 7950
  • Type: GPU
  • Bus: PCIe
  • Slot: Slot-1
  • PCIe Lane Width: x16
  • VRAM (Total): 3072 MB
  • Vendor: ATI (0x1002)
  • Device ID: 0x679a
  • Revision ID: 0x0000
  • ROM Revision: 113-E2080C-101
  • EFI Driver Version: 01.00.624
Click to expand...
 
thedocbwarren said:
That looks right, sadly mine doesn't. I guess it's ok for now but going to troubleshoot a bit more. Mine says 4x lane width.
Click to expand...

Is there any return window for your card? If yes, don’t diagnosis too long, as long as the cMP can run other card at x16 in the same slot, you better return it. Or at least apply a RMA. As you said, it’s not cheap, and brand new (from OWC???), why you want to pay big money for a may be damaged old card?

If the issue is just limited to x4 lane. Then not a huge problem at all, in fact, virtually make zero difference than a x16 card on cMP. But the worst part is that we don’t know if there is any other hidden trouble / damage.
 
Sadly no I never noticed till recently as I was sure I remember it saying 16x at one point before Sierra.

h9826790 said:
Is there any return window for your card? If yes, don’t diagnosis too long, as long as the cMP can run other card at x16 in the same slot, you better return it. Or at least apply a RMA. As you said, it’s not cheap, and brand new (from OWC???), why you want to pay big money for a may be damaged old card?

If the issue is just limited to x4 lane. Then not a huge problem at all, in fact, virtually make zero difference than a x16 card on cMP. But the worst part is that we don’t know if there is any other hidden trouble / damage.
Click to expand...
 
thedocbwarren said:
Sadly no I never noticed till recently as I was sure I remember it saying 16x at one point before Sierra.
Click to expand...

Sapphire should provide something like 2 years warranty for a brand new 7950 Mac Edition card. Their CS is actually OK. Quite helpful. May be you can try to open a ticket on their supporting page.
 
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