BigSur / OC : why is my Nvme GEN4 not at full speed ?


bjornatic

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Hello !

 

I'll try to keep it short :

Fresh BigSur install (with Macinabox) on a 256Gb Samsung 980 PRO with the controller passed through.

 

The drive is on now on a PCIe Gen 4 socket but it may important to note that it was (my mistake) on a GEN3 socket during the install.

 

So before I moved it to the right socket, "System Report" reported : Link width : 4x / Link Speed 8GT/s (so GEN 3).

 

Now, it's on the right socket, the lspci command gives : LnkSta:  Speed 16GT/s (ok), Width x4 (ok)

 

BUT, and this is the problem I can't find a solution / explanation for : under System Report, Link Width is still 4x but there is no info for Link Speed... ???

 

A Blackmagicdesign Disk Speed test shows a read speed of 2.8GB/s (so the same as on GEN3) where the drive is theoretically capable of 7GB/s. And I know I wont get that speed, but now I'm having less than half.

 

Other details :

The same drive passed through (controller) to a windows VM is on a GEN4 link. So all good on this side.

Motherboard is Asus TUF Gaming X570. Latest bios.

The XML part for the controller :

    <hostdev mode='subsystem' type='pci' managed='yes'>
      <driver name='vfio'/>
      <source>
        <address domain='0x0000' bus='0x04' slot='0x00' function='0x0'/>
      </source>
      <alias name='hostdev0'/>
      <address type='pci' domain='0x0000' bus='0x04' slot='0x00' function='0x0'/>
    </hostdev>

1937377602_Capturedecran2020-12-14a20_16_17.png.f19866abe9212caf52e15afe0951ed96.png

1412750913_Capturedecran2021-05-22a09_50_07.png.b05b982365c8146cda26a923fa233e1b.png

 

I even tried to move from Q35-4.2 to 5.1, but nothing changed.

 

My fear is that it's because I swapped socket after the install... And that the solution would be a new install... But maybe one of you will have a better suggestion !

Thanks for your attention.

 

 

Edited by bjornatic
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