GPU Debugging¶
GPUVM Debugging¶
To aid in debugging GPU virtual memory related problems, the driver supports a number of options module parameters:
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/SQC/SQG: Shaders
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 their shader code and resource descriptor state to determine what caused the GPU page fault.
UMR¶
umr is a general purpose GPU debugging and diagnostics tool. Please see the umr documentation for more information about its capabilities.