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z370 Taichi PCIe Question
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gregorskii View Drop Down
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    Posted: 23 Mar 2018 at 6:37am
Hi all,

Forgive me if this has been asked. I tried searching first.

I have a 8700k and a z370 taichi running the most up to date firmware.

Per the manual I am supposed to put my GTX 1080 in the upper most PCIE (PCIe2) slot near the processor.

If I do this GPUZ reports that the bus is running at "PCIe x16 3.0 @ 1x 3.0" and 3dmark / game framerates are half what they should be.

If it put the card in the middle silver slot (PCIe4) the bus speed reports as "PCIe x16 3.0 @ 8x 3.0" framerates are doubled and 3dmark is much higher (+1000 on Time Spy).

Per the manual a single PCIe card is supposed to go in PCIE2.

The only other PCIE devices I am using are 3x m2 drives total in the MOBO slots.

Am I doing something incorrect, or am I missing a setting?

With the card in the lower slot, graphics are fine and all m2 drives appear to work.

Let me know what other information you may need in debugging this.

Thanks
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wardog View Drop Down
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Points: 6447 		Post Options Post Options   Thanks (0) Thanks(0)   Quote wardog Quote  Post ReplyReply Direct Link To This Post Posted: 23 Mar 2018 at 7:20am
Running out of PCIe Lanes is my guess.

The 8700K offers 16, yet depending on just how many those three M.2 drives are using will limit out, fast.
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gregorskii View Drop Down
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I thought the z370 chip handles the m2s?

http:// www.overclock.net/forum/6-intel-motherboards/1640221-z370-8700k-m-2-pcie-question-about-pcie-lanes-sharing.html 

Also why would slot 2 run at 1x? But slot 2 runs correctly at 8x.
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gregorskii View Drop Down
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I talked over the phone with support, they suggested re-seating the CPU and checking the mobo for shorts.

If that doesn't work RMA it.
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wardog View Drop Down
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Points: 6447 		Post Options Post Options   Thanks (0) Thanks(0)   Quote wardog Quote  Post ReplyReply Direct Link To This Post Posted: 23 Mar 2018 at 8:31am
They are sometime quick to RMA IMO.

Here's how I understand it, and sorry for the late reply.

https://linustechtips.com/main/topic/869979-m2-disrupt-pcie-lanes/?tab=comments#comment-10792063
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gregorskii View Drop Down
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I think thats referring to how the chipset controls its own lanes. If it were the case (at worst) that using ANY mobo PCIe lane would cut off 4 lanes to the processor. If that were the case no one could run anything from the chipset without blocking the processor from running 16 lanes. It would be at best 12.

I think the 4 lanes between the chipset and the processor are dedicated... I mean assumptions here.. but they have to be. Otherwise ANYONE using a single m2 drive would lose x16 on the main PCIe gfx port.

It still would not explain why the card gets x8 from the lower x8 slot. If it were sucking 4 lanes from the 16 to run the chipset the top slot would run at x8.

I reseated the processor / cpu cooler / checked for any damage to the CPU / mobo. No bent pins, no marks on the CPU dots.

It all looks fine.

Re-seated, put card in slot 2 its x1.

Does anyone know if there is something in bios that can control this?

I have already cleared CMOS and reset up my settings, changed nothing.

I see from reading other issues Asus mobos show you the lanes in bios for each slot. The bios for the Taichi does not have any section related to this.

The only setting I see is the PCIe slot link speed. Which I have tried auto and gen3 on slot2. Slot 4 is on auto and works at x8.

I am thinking there is either something inherently wrong with the controller in this processor (doubtful?) or this mobo needs an RMA.

Any other ideas?

Thanks.


Edited by gregorskii - 23 Mar 2018 at 9:11am
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badbri View Drop Down
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When you run GPU Z did you click the ? (next to Bus interface) and do the Render Test ?
If you did and it reports @1X, not @16x then it sounds like first PCIe slot is damaged and you should RMA it.
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wardog View Drop Down
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Originally posted by badbri badbri wrote:

When you run GPU Z did you click the ? (next to Bus interface) and do the Render Test ?
If you did and it reports @1X, not @16x then it sounds like first PCIe slot is damaged and you should RMA it.


Good point.
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gregorskii View Drop Down
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Yes I did. From what I understand this only changes the generation. The system downclocks when not under load to use 1.1.

I have done every recommended option for fixing this from the graphics config side. Putting the card in slot 4 immediately reports x8 regardless of whether the card is under load. Slot 2 reports x1 no matter what.

You can see my back and forth on EVGA forums here: https ://forums.evga.com/1080-SC-Performance-m2806455.aspx

I also tried removing all but one m2 drive, still x1.
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Xaltar View Drop Down
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Is this a large, heavy GPU?

I saw a post on another forum just recently with this same issue and it turned out that the GPU was sagging and it was causing poor contact along the top edge of the GPU nearest the front of the case. PCIe slots are set up by length for the different lane configs, 1x is the first small section nearest the rear of the case, x2 a little closer to the front of the case and so on till you get to x16 which is the last third or so of the slot. The device will work even if only the x1 portion is making contact. This leads many to believe the card is properly seated and to dismiss the slot fit as a potential source for the issue.

Try supporting the GPU on a small box or some such that keeps it exactly level or very, very slightly tilted up at the end. See if that gives you your full x16.

I am not sure exactly why but x8 wired slots tend to be a more snug fit for some reason, possibly due to fewer traces and less applied heat at the end of the slot during manufacture. 

Let us know if this helps.
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