GTX 1080 only has 8 PCIE 3.0 lanes (not 16) but seems to run OK - should I be worried?

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myNamesTaken

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Looking at HWInfo, I see that my GTX 1080 is only accessing 8 PCIE 3.0 lanes (at 2.5 GT/s) bandwidth, vs the possible 16 lanes at 8.0 GT/s bandwith, I think because I'm using a sm951 drive that steals some lanes on my board (ASRock z97 Extreme 6).
Should I worry about this?

Some background:
I built my machine with development aims in mind, not wanting to game on it (so the sm951 speed was worth loosing some graphics lanes then). I still am doing development work on this machine but I'm wanting to start gaming at some point - probably VR, hence I added a GTX 1080 (I had just been using integrated graphics).

When I performance test the rig for VR (using steam's app) it does amazingly well, hence I think it's probably fine as it is.

But I haven't tested any regular games on it, so I just wondered - would others be worried by loosing that bandwith on the graphics card, or confortable that 8 lanes / 2.5 GT/s is pleenty to work with? I could e.g. consider selling the drive, reinstalling the OS on drive that didn't tax the graphics bandwith like this.

Thanks for any help.
 
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ya, ok so like I said above the m2 is shared with the cpu and not the chipset see some intel boards are that way some may not

just like my asrock z87 will reduce to 8x4x4

so I can see the m2 being the issue

well I thought I covered that above but I must of thought of another thread - man am I getting old and careless I guess I'm loosing it [lol]... sorry


''In order to equip the motherboard with an M.2 x4 port, ASRock had two choices. They could combine four lanes from the chipset/PCH into a single slot, although that would severely limit the number of controllers that could be placed on the motherboard without additional PCIe switches. The other method was in the x8/x4/x4 allocation from the CPU, earmarking the final...
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junkeymonkey

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now at idle that is right but under load it should jump up to 8 ? at least mine will

let me post a screen shot in a min hang on

WR4Q9zF.jpg


that's current -min - max - and average

so at idle its 2.5 but when I put a load on the card like just that gpu-z render test it goes to 8,0 then when the card goes back to no load and idle it falls back to 2.5
 
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myNamesTaken

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Thanks junkeymonkey - if your looking at PCIE link speed line in the sensor status mine is 2.5 GT/s for every column (current min max av). I haven't done much at all on the machine yet that would put the graphics under load - played a little of one steam game online. Am I looking in the right place? What are you using to put a load on the GPU? Thanks



 
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myNamesTaken

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Thanks ancient - good thought. For this mobo a single 16 lane pcie graphics card goes into the PCIE2 slot which is where the card is. The documentation warns that if you use a drive like the sm951 it will steal some of the pcie lanes that would otherwise be available to a graphics card, so I don't think there's anything unexpected in this.



 
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junkeymonkey

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gpu-z and its render test for that - these cards will ''downclock '' or keep a low power state until you put a load to them then they will ''boost'' up

when the card is just doing nothing much like just at desk top its not needing to run full power so its clocks are down and things are at pcie 1.1 specs then you load the card and it will [should] jump up to full pcie 3.0 specs .

see the ''?'' mark in my screenshot at the end of the bus interface spot click on it and the test will start

https://www.techpowerup.com/gpuz/



''ASRock z97 Extreme 6''' I'm using a ASRock z87 Extreme 6

''HWiNFO64''

https://www.hwinfo.com/download.php
 
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myNamesTaken

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Thanks junkeymonkey:
after the render test on GPU-z, the GPU goes up to *8 3.0 and HwInfo shows PCIe v3.0 x16 (8.0 GT/s) @ x8 (8.0 GT/s).
So with these results - all is good, I should be happy?
I would like to keep using the sm951 and would only really think about swapping it out if I'm not likely to get a good vr experience with this rig?
(I'm not planning on getting the VR equipment for a little while yet.)
Kind regards.



 
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junkeymonkey

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if you got just the one card in and nothing is sharing the lanes from off the cpu it should be x16 not x8 ..

rsUsZsL.jpg



the screen shot I gave above was at idle and see its at x16 1.1 but under load as above it jumps to x16 at 3.0 [ no where at 8x ]

maybe contact the manufactures support on that should be at full x16 not x8

this is what you need to test it in another computer to insure it the card at fault ?

''Update : I got my 2nd gtx 780ti last week its runs in x16 link, the first card only runs in 8x

http://forums.evga.com/GTX-780-TI-running-in-x8-link-m2106118.aspx

 
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myNamesTaken

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Hi junkeymonkey,
if you look at this review of the samsung xp941 in an asrock z97 extreme 6 board the issue is discussed (my sm951 drive goes in the ultra m2 slot as well): http://www.tomshardware.com/reviews/samsung-xp941-z97-pci-express,3826-3.html
The key bit is quoted below (inside '== ...==').
What I'm trying to work out is - is it possible the performance will be ok even with 8 lanes lost to the graphics card? The steam vr performance test seems to say so.
Thanks again.
===
Of course, as we've established, ASRock's Z97 Extreme6 is unique. It does have a two-lane M.2 PCI Express 2.0 slot competing for the PCH's limited bandwidth. But it also employs what ASRock calls Ultra M.2, which is a second slot tapping into a Haswell-based CPU's 16 lanes of third-gen PCIe, too. This slot isn't affected by the chipset. And if you drop a PCIe M.2 drive into the Ultra slot, you can still use SATA Express, which is wired into Z97. In exchange, you can't run a graphics card using the processor's 16 lanes, instead bumping it down to eight. Perhaps more severely, SLI and CrossFire configurations are out, too.
===




 
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junkeymonkey

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ya, ok so like I said above the m2 is shared with the cpu and not the chipset see some intel boards are that way some may not

just like my asrock z87 will reduce to 8x4x4

so I can see the m2 being the issue

well I thought I covered that above but I must of thought of another thread - man am I getting old and careless I guess I'm loosing it [lol]... sorry


''In order to equip the motherboard with an M.2 x4 port, ASRock had two choices. They could combine four lanes from the chipset/PCH into a single slot, although that would severely limit the number of controllers that could be placed on the motherboard without additional PCIe switches. The other method was in the x8/x4/x4 allocation from the CPU, earmarking the final x4 for the M.2. In this method, installing an M.2 drive in this x4 slot would reduce any chipset overhead, but it would also reduce the other PCIe lanes down to x8/x4. This removes any chance of SLI, but Crossfire can still be used in x8/x4. ''

http://www.anandtech.com/show/8045/asrock-z97-extreme6-review-ultra-m2-x4-tested-with-xp941

so with that all now seems correct on your x8 issue [nonissue] and your good to go

 
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