[PATCH] Documentation: add a page on amdgpu debugging

[Friedrich Vock]

On 13.03.24 22:01, Alex Deucher wrote:
> Covers GPU page fault debugging and adds a reference
> to umr.
>
> Signed-off-by: Alex Deucher<alexander.deucher at amd.com>
> ---
>   Documentation/gpu/amdgpu/debugging.rst | 79 ++++++++++++++++++++++++++
>   Documentation/gpu/amdgpu/index.rst     |  1 +
>   2 files changed, 80 insertions(+)
>   create mode 100644 Documentation/gpu/amdgpu/debugging.rst
>
> diff --git a/Documentation/gpu/amdgpu/debugging.rst b/Documentation/gpu/amdgpu/debugging.rst
> new file mode 100644
> index 000000000000..29971a7a6815
> --- /dev/null
> +++ b/Documentation/gpu/amdgpu/debugging.rst
> @@ -0,0 +1,79 @@
> +===============
> + GPU Debugging
> +===============
> +
> +GPUVM Debugging
> +===============
> +
> +To aid in debugging GPU virtual memory related problems, the driver supports a
> +number of options module paramters:
> +
> +`vm_fault_stop` - If non-0, halt the GPU memory controller on a GPU page fault.
> +
> +`vm_update_mode` - If non-0, use the CPU to update GPU page tables rather than
> +the GPU.
> +
> +
> +Decoding a GPUVM Page Fault
> +===========================
> +
> +If you see a GPU page fault in the kernel log, you can decode it to figure
> +out what is going wrong in your application.  A page fault in your kernel
> +log may look something like this:
> +
> +::
> +
> + [gfxhub0] no-retry page fault (src_id:0 ring:24 vmid:3 pasid:32777, for process glxinfo pid 2424 thread glxinfo:cs0 pid 2425)
> +   in page starting at address 0x0000800102800000 from IH client 0x1b (UTCL2)
> + VM_L2_PROTECTION_FAULT_STATUS:0x00301030
> + 	Faulty UTCL2 client ID: TCP (0x8)
> + 	MORE_FAULTS: 0x0
> + 	WALKER_ERROR: 0x0
> + 	PERMISSION_FAULTS: 0x3
> + 	MAPPING_ERROR: 0x0
> + 	RW: 0x0
> +
> +First you have the memory hub, gfxhub and mmhub.  gfxhub is the memory
> +hub used for graphics, compute, and sdma on some chips.  mmhub is the
> +memory hub used for multi-media and sdma on some chips.
> +
> +Next you have the vmid and pasid.  If the vmid is 0, this fault was likely
> +caused by the kernel driver or firmware.  If the vmid is non-0, it is generally
> +a fault in a user application.  The pasid is used to link a vmid to a system
> +process id.  If the process is active when the fault happens, the process
> +information will be printed.
> +
> +The GPU virtual address that caused the fault comes next.
> +
> +The client ID indicates the GPU block that caused the fault.
> +Some common client IDs:
> +
> +- CB/DB: The color/depth backend of the graphics pipe
> +- CPF: Command Processor Frontend
> +- CPC: Command Processor Compute
> +- CPG: Command Processor Graphics
> +- TCP: Shaders

For shader accesses, maybe including SQC (data)/SQC (inst) for SMEM
accesses/instruction prefetching would be useful?

Thanks,
Friedrich

> +- SDMA: SDMA engines
> +- VCN: Video encode/decode engines
> +- JPEG: JPEG engines
> +
> +PERMISSION_FAULTS describe what faults were encountered:
> +
> +- bit 0: the PTE was not valid
> +- bit 1: the PTE read bit was not set
> +- bit 2: the PTE write bit was not set
> +- bit 3: the PTE execute bit was not set
> +
> +Finally, RW, indicates whether the access was a read (0) or a write (1).
> +
> +In the example above, a shader (cliend id = TCP) generated a read (RW = 0x0) to
> +an invalid page (PERMISSION_FAULTS = 0x3) at GPU virtual address
> +0x0000800102800000.  The user can then inspect can then inspect their shader
> +code and resource descriptor state to determine what caused the GPU page fault.
> +
> +UMR
> +===
> +
> +`umr<https://gitlab.freedesktop.org/tomstdenis/umr>`_ is a general purpose
> +GPU debugging and diagnostics tool.  Please see the umr documentation for
> +more information about its capabilities.
> diff --git a/Documentation/gpu/amdgpu/index.rst b/Documentation/gpu/amdgpu/index.rst
> index 912e699fd373..847e04924030 100644
> --- a/Documentation/gpu/amdgpu/index.rst
> +++ b/Documentation/gpu/amdgpu/index.rst
> @@ -15,4 +15,5 @@ Next (GCN), Radeon DNA (RDNA), and Compute DNA (CDNA) architectures.
>      ras
>      thermal
>      driver-misc
> +   debugging
>      amdgpu-glossary