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Graphics Card Drops from x16 to x8 (AMD = PCI-E 2.0) when cpu overclocked.

post #1 of 24
Thread Starter 
Hi, I can't figure this out for my life. When I leave my computer at stock (3.4)ghz my GPU uses pci-e 2 x16, but when I overclock to 3.9 the lane drops to x8. AMD don't do 3.0 and my 7970 needs the throughput. What could cause this?
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post #2 of 24
Is your graphics card in one of the fist two slots? Try moving the graphics card to the first PCI-E slot on your motherboard (closest to the CPU) if it isn't already. Also, try starting Furmark or similar GPU stressing utility and check whether GPU-Z still reports your card to be working on a PCI-E 8x lane. It is possible that, due to power saving reasons, this can be reported in idle state, but under stress it will be x16 (at least so I've heard).
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post #3 of 24
Thread Starter 
Thanks but I have 5 PCI-E 2.0 x16 slots, and can use the main 2 simultaneously at x16 (1 and 5). I have tried it in slot 1, same issue. Slot 1 is too close to my massive CPU cooler so I leave it in slot 5, both of which produce x16 when puter not OC'd.

When rig is overclocked:

The GPU at rest (idle) reads as: Bus Interface "PCI-E 3.0 x16 @ x8 1.1" and the clocks are at core 300mhz and mem 150mhz.

When I put it to work The Bus Interface jumps to "PCI-E 3.0 x16 @ x8 2.0" and the clocks go back up to 1000mhz and 1500mhz.

So it's not a card at rest issue. When I'm not overclocked, at rest/idle the Bus Interface read "PCI-E 3.0 x16 @ x16 1.1"
and in use "PCI-E 3.0 x16 @ x16 2.0" as it should be. (thanks AMD! why would a mobo advertise PCI-E 3.0 when it's AMD and can only use 2.0? anyways) and the clocks go back up to 1000mhz and 1500mhz. Not a power saving or slot issue. Something in the BIOS might be choking the lane? The obvious stuff I ruled out. That I don't know how voltages and speeds mix and affect things is where I'm lost and think the problem is.

I can switch from regular to overclock with one simple BIOS selection. Regular x16, OC'd x8, never fails, it's like switch lol.

I can't seem to add pics or I would show my BIOS settings, someone might see something...sigh
Edited by Darkhaze - 5/15/14 at 8:20am
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post #4 of 24
are you sure it was ad as 3.0?

anyway, the difference between 2.0 and 3.0 is nill, especially with single cards.
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post #5 of 24
Thread Starter 
The card is read as capable of 3.0 x16, amd boards don't have 3.0, only 2.0. 2.0 uses much more overhead, still while at x16, which is equal to 3.0 x8 (but don't forget the massive overhead), I agree no big. but 2.0 x8 (less than equal to 3.0 x4)... That's a bottleneck for my card.

If a games is CPU heavy I play it with rig OC'D, if it's GPU heavy, I play it stock settings and just OC the GPU (which doesn't drop me from x16 to x8 btw). I shouldn't have to choose... everytime...
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post #6 of 24
It's probably a motherboard issue. Target that. The motherboard.
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post #7 of 24
Thread Starter 
As much as I'd like to put a shotgun to it, i need a more accurate strategy. It's certainly the motherboard settings... but that's a fairly complex web and I don't know which strand(s) I need to be looking at.
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post #8 of 24
Oh yeah. I meant I'd try the motherboard forum, or the company. Etc.
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post #9 of 24
Quote:
Originally Posted by Darkhaze View Post

The card is read as capable of 3.0 x16, amd boards don't have 3.0, only 2.0. 2.0 uses much more overhead, still while at x16, which is equal to 3.0 x8 (but don't forget the massive overhead), I agree no big. but 2.0 x8 (less than equal to 3.0 x4)... That's a bottleneck for my card.

If a games is CPU heavy I play it with rig OC'D, if it's GPU heavy, I play it stock settings and just OC the GPU (which doesn't drop me from x16 to x8 btw). I shouldn't have to choose... everytime...

Dark, i'm not into sugar coating. that 3.0 vs 2.0 issue nothing compared to the kinda of bottleneck the cpu exact on the 7970. i say - don't worry about it.

Verify if the board allows 3.0. if you are using GPUZ, then it could be reading the 7970, which is 3.0. not sure . . . just guessing. but you are right, it should not go from 16 to 8.
Edited by rdr09 - 5/15/14 at 9:22am
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post #10 of 24
Thread Starter 
Good thinking, I had meant to put in the motherboard forum too... but I didn't - I was high, but there might have been a reason, but it may not have been a good one wink.gif
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