1=============== 2 GPU Debugging 3=============== 4 5GPUVM Debugging 6=============== 7 8To aid in debugging GPU virtual memory related problems, the driver supports a 9number of options module parameters: 10 11`vm_fault_stop` - If non-0, halt the GPU memory controller on a GPU page fault. 12 13`vm_update_mode` - If non-0, use the CPU to update GPU page tables rather than 14the GPU. 15 16 17Decoding a GPUVM Page Fault 18=========================== 19 20If you see a GPU page fault in the kernel log, you can decode it to figure 21out what is going wrong in your application. A page fault in your kernel 22log may look something like this: 23 24:: 25 26 [gfxhub0] no-retry page fault (src_id:0 ring:24 vmid:3 pasid:32777, for process glxinfo pid 2424 thread glxinfo:cs0 pid 2425) 27 in page starting at address 0x0000800102800000 from IH client 0x1b (UTCL2) 28 VM_L2_PROTECTION_FAULT_STATUS:0x00301030 29 Faulty UTCL2 client ID: TCP (0x8) 30 MORE_FAULTS: 0x0 31 WALKER_ERROR: 0x0 32 PERMISSION_FAULTS: 0x3 33 MAPPING_ERROR: 0x0 34 RW: 0x0 35 36First you have the memory hub, gfxhub and mmhub. gfxhub is the memory 37hub used for graphics, compute, and sdma on some chips. mmhub is the 38memory hub used for multi-media and sdma on some chips. 39 40Next you have the vmid and pasid. If the vmid is 0, this fault was likely 41caused by the kernel driver or firmware. If the vmid is non-0, it is generally 42a fault in a user application. The pasid is used to link a vmid to a system 43process id. If the process is active when the fault happens, the process 44information will be printed. 45 46The GPU virtual address that caused the fault comes next. 47 48The client ID indicates the GPU block that caused the fault. 49Some common client IDs: 50 51- CB/DB: The color/depth backend of the graphics pipe 52- CPF: Command Processor Frontend 53- CPC: Command Processor Compute 54- CPG: Command Processor Graphics 55- TCP/SQC/SQG: Shaders 56- SDMA: SDMA engines 57- VCN: Video encode/decode engines 58- JPEG: JPEG engines 59 60PERMISSION_FAULTS describe what faults were encountered: 61 62- bit 0: the PTE was not valid 63- bit 1: the PTE read bit was not set 64- bit 2: the PTE write bit was not set 65- bit 3: the PTE execute bit was not set 66 67Finally, RW, indicates whether the access was a read (0) or a write (1). 68 69In the example above, a shader (cliend id = TCP) generated a read (RW = 0x0) to 70an invalid page (PERMISSION_FAULTS = 0x3) at GPU virtual address 710x0000800102800000. The user can then inspect their shader code and resource 72descriptor state to determine what caused the GPU page fault. 73 74UMR 75=== 76 77`umr <https://gitlab.freedesktop.org/tomstdenis/umr>`_ is a general purpose 78GPU debugging and diagnostics tool. Please see the umr 79`documentation <https://umr.readthedocs.io/en/main/>`_ for more information 80about its capabilities. 81