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Disabling ECC (Pro VRAM)

WIP: Procedure is documented for Radeon PRO W6800 in lunnova’s guide. #vllm-rdna and #general report the same ECC-on-by-default behavior on V620. Treat the two-reboot kernel-param path as community until you confirm rocm-smi on your own cards. See Verification status.

Workstation/data-center Navi 21 cards (PRO V620, PRO W6800) ship with on-board ECC enabled. That costs about 7% of VRAM (~2 GB on a 32 GB card). Consumer RX 6800 / 6900 cards have no ECC and already show the full 16 GB.

ECCTypical rocm-smi VRAM (32 GB Pro card)
On (factory default)~30 700 MiB (~30 GB)
Off~32 768 MiB (full 32 GB)

#vllm-rdna (pinned): extra ~2 GB per GPU if you disable it. Some members keep ECC on for bit-flip protection; others disable it for long-context KV cache.

Check whether ECC is on

sudo dmesg | grep -i ecc
# "MEM ECC is active" / "GECC is enabled"  → ECC is on
# "MEM ECC is not presented"               → consumer card / no ECC

rocm-smi --showmeminfo vram
# ~30.7 GB total on a 32 GB Pro card → ECC is eating the rest

Linux: amdgpu.ras_enable=0 (two reboots)

There is no Radeon control-panel toggle on Linux. The community path (lunnova, 6.x kernels) is:

  1. Add the kernel parameter amdgpu.ras_enable=0.
  2. Reboot twice, leaving the parameter in place both times.

GRUB (Ubuntu / Debian / Fedora):

# Ubuntu/Debian: edit GRUB_CMDLINE_LINUX_DEFAULT in /etc/default/grub
# Fedora: sudo grubby --update-kernel=ALL --args="amdgpu.ras_enable=0"
sudo nano /etc/default/grub
# …add amdgpu.ras_enable=0 to GRUB_CMDLINE_LINUX_DEFAULT, then:
sudo update-grub   # Ubuntu/Debian
# Fedora uses grubby above instead of update-grub
sudo reboot

After the first reboot, dmesg should mention that GECC will be disabled on the next boot:

GECC will be disabled in next boot cycle if set amdgpu_ras_enable and/or amdgpu_ras_mask to 0x0

Reboot again. On the second boot you want:

amdgpu: GECC is disabled

and rocm-smi --showmeminfo vram should report the full ~32 768 MiB.

To turn ECC back on: remove the kernel parameter and reboot twice.

An older amdgpu-no-ecc.patch is not needed on 6.x kernels. Keep it only if you are still on 5.x and the two-reboot path does nothing — details in lunnova’s article.

Notes

  • Consumer gfx1030 (RX 6800 / 6800 XT / 6900 XT / 6950 XT): skip this page.
  • Secure Boot / signed kernels: same caveats as power tuning — unsigned module overrides will not load.
  • This does not replace the 120 W power-cap patch. ECC and the VBIOS power floor are independent.