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feat(dankclaw): boot with iommu=pt — identity DMA, IOMMU stays armed

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The 2026-09-11 trade bought a vendor-claimed 13-16% prefill figure that was
never measured here; the 2026-10-18 research (same decision record) shows what
identity mode actually costs the iGPU is the 1:1 page walk plus ATS/PRI/PASID/
GCR3 -- worth 2-4% on this silicon class, and removable outright by AMD PerfOpt
when the distro ships Linux 7.4. Meanwhile pt is what err=-19 asks for: the
XDNA2 NPU binds its own IOPT_TYPE_SVA domain and only needs the IOMMU enabled.

Measured off-vs-pt prefill arms follow in the docs commit; frank-archon
(Dankserver) is untouched.
This commit is contained in:
Frank
2026-10-18 01:22:59 -07:00
parent 47a5f5582e
commit 1b373f3559
1 changed files with 5 additions and 2 deletions
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dankclaw/host/grub
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@@ -7,8 +7,11 @@ GRUB_DEFAULT=0
GRUB_TIMEOUT_STYLE=hidden GRUB_TIMEOUT_STYLE=hidden
GRUB_TIMEOUT=0 GRUB_TIMEOUT=0
GRUB_DISTRIBUTOR=`( . /etc/os-release && echo ${NAME} )` GRUB_DISTRIBUTOR=`( . /etc/os-release && echo ${NAME} )`
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash amd_iommu=off" # Identity (passthrough) DMA since 2026-10-18: the IOMMU stays enabled, so the
GRUB_CMDLINE_LINUX="" # XDNA2 NPU (/dev/accel/accel0, PASID/SVA) is usable again, while the iGPU's DMA
# runs untranslated. Decided in serverAppConfigs-docs/LLM/
# dankclaw-iommu-translation-off.md; install with scripts/set-dankclaw-bootline.sh.
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash iommu=pt"
# If your computer has multiple operating systems installed, then you # If your computer has multiple operating systems installed, then you
# probably want to run os-prober. However, if your computer is a host # probably want to run os-prober. However, if your computer is a host