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[Rant]: RX 5700... a frustrating experience
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Shmerl 5 Jul
Quoting: CybolicI will mention: upgrade your BIOS before you plug in your card! I couldn't get the BIOS to boot before that and now I have to fix GRUB because the update hosed UEFI, so do remember that extra step if you're getting one of these lovely new cards.

You can also enable resizable BAR in UEFI for better performance with the new card.

lspci -vv gives me this after it's enabled:

        Capabilities: [200 v1] Physical Resizable BAR
                BAR 0: current size: 16GB, supported: 256MB 512MB 1GB 2GB 4GB 8GB 16GB
                BAR 2: current size: 256MB, supported: 2MB 4MB 8MB 16MB 32MB 64MB 128MB 256MB
Cybolic 5 Jul
Quoting: Shmerl[...]You can also enable resizable BAR in UEFI for better performance with the new card.
I had done that already actually, but it turns out I also needed to disable CSM support for it to take effect. So, thanks for making me double check!

Side-note, I'm really surprised at how much of a difference an AMD card makes in just standard use! The system boots faster, X starts faster, windows switch faster (on bspwm, no less) and fonts somehow look better! (there seems to be a minor difference in DPI scaling, but it really does look better).

I gotta say, I'm very impressed! Also, being able to run Resident Evil 2 HD at high settings without being able to hear the GPU is really quite something :D
I know the card I got is overkill in general (PowerColor RX 6900 XT Ultimate), but I still wasn't expecting this level of greatness and difference coming from a 2080 Ti!
Shmerl 5 Jul
I had a bit of rough time with Sapphire Pulse RX 5700 XT in the past, but I'm surprised how well their Pulse RX 6800 XT runs out of the box.

In general though when I switched from Nvidia to AMD (in Polaris time still with RX 480) it felt very good indeed because of much better integrated experience.

Last edited by Shmerl on 5 July 2021 at 8:44 pm UTC
Dragunov 3 years 7 Jul
I would like to enable the resizable BAR, but enabling it causes my PCI-E Wifi card to stop working. It is then no longer detected by the system until I disable it again.
Shmerl 7 Jul
Quoting: DragunovI would like to enable the resizable BAR, but enabling it causes my PCI-E Wifi card to stop working. It is then no longer detected by the system until I disable it again.

If it's Intel (probably the only decent WiFi driver), you can open a bug in the kernel bug tracker.
Dragunov 3 years 9 Jul
Well, the problem is that it happens in Windows 10 as well. Its a TP-Link Archer T5E and it is using an Intel Chip. The PC works great as it stands, so I'm not too worried about it.

Last edited by Dragunov on 9 July 2021 at 1:54 am UTC
Quoting: ShmerlYou can also enable resizable BAR in UEFI for better performance with the new card.
afaik you don't need a special bios option to toggle reBAR , bridgeman on Phoronix forums told me that. I have a b350 that in theory has no hardware support for ReBAR, but it doesn't matter because it's done via software
[    1.351339] amdgpu 0000:08:00.0: amdgpu: Fetched VBIOS from ROM BAR
[    1.351442] amdgpu 0000:08:00.0: BAR 2: releasing [mem 0xf0000000-0xf01fffff 64bit pref]
[    1.351446] amdgpu 0000:08:00.0: BAR 0: releasing [mem 0xe0000000-0xefffffff 64bit pref]
[    1.351474] pcieport 0000:07:00.0: BAR 15: releasing [mem 0xe0000000-0xf01fffff 64bit pref]
[    1.351476] pcieport 0000:06:00.0: BAR 15: releasing [mem 0xe0000000-0xf01fffff 64bit pref]
[    1.351478] pcieport 0000:03:04.0: BAR 15: releasing [mem 0xe0000000-0xf01fffff 64bit pref]
[    1.351479] pcieport 0000:02:00.2: BAR 15: releasing [mem 0xe0000000-0xf01fffff 64bit pref]
[    1.351480] pcieport 0000:00:01.3: BAR 15: releasing [mem 0xe0000000-0xf01fffff 64bit pref]
[    1.351489] pcieport 0000:00:01.3: BAR 15: assigned [mem 0x500000000-0x7ffffffff 64bit pref]
[    1.351491] pcieport 0000:02:00.2: BAR 15: assigned [mem 0x500000000-0x7ffffffff 64bit pref]
[    1.351493] pcieport 0000:03:04.0: BAR 15: assigned [mem 0x500000000-0x7ffffffff 64bit pref]
[    1.351495] pcieport 0000:06:00.0: BAR 15: assigned [mem 0x500000000-0x7ffffffff 64bit pref]
[    1.351496] pcieport 0000:07:00.0: BAR 15: assigned [mem 0x500000000-0x7ffffffff 64bit pref]
[    1.351498] amdgpu 0000:08:00.0: BAR 0: assigned [mem 0x600000000-0x7ffffffff 64bit pref]
[    1.351510] amdgpu 0000:08:00.0: BAR 2: assigned [mem 0x500000000-0x5001fffff 64bit pref]
[    1.351608] [drm] Detected VRAM RAM=6128M, BAR=8192M


for AMD you don't need any special hardware I think that polaris supports it too, it's done through the amdgpu kernel module.
Maybe there's a difference between Physical ReBAR, and what looks like in my case as Software ReBAR... don't know really.
As you can see I have 6GB of VRAM, but I can use 8GB with reBAR. I suppose it uses 2GB of standard RAM to complete the remaining.
Most likely if you were on AMD this years, you would have had reBAR enabled by the kernel module and you didn't notice, it doesn't require any toggling in the BIOS, it's just Nvidia that's late to the party.
Also problem with ReBAR is that the Mesa driver doesn't take advantage of this feature that much. Only RDNA2 cards have mesa features implemented to take advantage of ReBAR, but that stuff can be ported to older cards for sure.

Last edited by The_Aquabat on 9 July 2021 at 5:47 am UTC
Shmerl 9 Jul
Some info here.

Looks like you still need to enable the option in the BIOS if you have it. Sometimes it's just not exposed or enabled by default.

Last edited by Shmerl on 9 July 2021 at 7:37 am UTC
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