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Is CPU PCIe faster than Chipset PCIe?

Discussion in 'Processors and motherboards Intel' started by MegaFalloutFan, Jan 12, 2018.

  1. MegaFalloutFan

    MegaFalloutFan Master Guru

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    Question, I have z370 motherboard: Is there any difference for PCIe storage performance between using Chipset routed slot or CPU routed slot?
    The only problem is if I use CPU routed PCIe, my video card will switch down from x16 to x8, but i heard that it shouldn't affect gaming performance for single 1080ti?
     
  2. mbk1969

    mbk1969 Ancient Guru

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    General consensus about x16 vs x8 is you should not notice difference.

    And of course CPU routed slot should work somewhat faster, but not twice faster.
     
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  3. MegaFalloutFan

    MegaFalloutFan Master Guru

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    Thats what i tough too, and googled other sources, everyone says that no difference between PCIe3 x8 and x16 for single GPU,
    but then i encountered this video, he talks too much but just look at his benchmark, the GPU score, the difference is huge.
    Maybe hes doing soothing wrong?

     
  4. mbk1969

    mbk1969 Ancient Guru

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    Not twice better though. I have never bothered with benchmarks so can`t comment on their usage.
     

  5. Hilbert Hagedoorn

    Hilbert Hagedoorn Don Vito Corleone Staff Member

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    No, the fastest NVMe SSDs utilizes a x4 link (which they never max out). When added into a PCIe slot tied to the CPU yes your GPU would tie in at x8 PCIe. Bus utilization on x8 PCIe Gen 3 is merely a few % of the total bandwidth available.

    For graphics, it could only pose an issue in SLI/CFX mode when one card is seated on a x16 chipset linked slot. There it would bog down to x4 perf due to the limited DMI interconnect between the CPU and chipset. This is why all graphics solutions run over the processor PCIe lanes and will split to x8/x8 on Z370/Coffee Lake - which still is fine bandwidth for any graphics cards. If you forcefully place a fast graphics card in the wrong PCIe slot that is linked over the chipset and both need to communicate with each other (multi-gpu), that's where you'd see the performance drop. In the past, this is why some motherboard manufacturers added a PLX chip on the mobo, to create more PCIe lanes for SLI/CFX locally (which still added a bit of latency).

    Long story short, you should not see a noticeable performance drop with storage and a GPU on the processor PCIe lanes.

    BTW an old test by now but testing in-between PCIe Generations showed this on bus utilization and how low it really is:

    http://www.guru3d.com/articles-pages/pci-express-scaling-game-performance-analysis-review,1.html
     
    Last edited: Jan 12, 2018
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  6. MegaFalloutFan

    MegaFalloutFan Master Guru

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    Thanks for replay, does it also apply to xpoint drives?
    I just got the 480gb one and need to decide where to stick it for best results :)
     
  7. 386SX

    386SX Member Guru

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    What do you mean by "best results"?
    As HH said (btw.: I was about to link to exactly the same article regarding the effect of limiting PCIe bandwidth, hehe), GFX won't be slowed down under normal circumstances, you may run your GFX by PCIe 3.0 x8 and only notice a few FPS dropping down, but nothing to be worried about. (Read his article, it is explained VERY GOOD!!)

    The "way of data" obviously is shorter if connected to the "CPU PCIe slots" instead of the "chipset PCIe slots". Data has to reach the CPU, the chipset is connected to the CPU. So if you connect anything to the chipset ones, the way (to the CPU) is longer instead of connecting the same device to the CPU PCIe slots, therefore it will give you some additional "delay". It may depend on your specific system on how much delay it will cause. How about you try it out? I did the same (testing PCIe slots) with my Intel 750 Pro and switched slots the one way and back. Even if you installed your OS on it, the drive is still bootable when placed to another slot, so do not worry about breaking anything.

    I would priorize your GFX instead of your SSD to be honest if differences are only small or unnoticable, becuase your GFX is "always working", your SSD more often has a break and idles. But if you notice a serious breakdown of your SSD (say for example 200MB instead of 500MB per second) I would priorize your SSD, sure.

    The whole package matters, not only one component. ;-)
     

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