Debug Failing Gpu

Debug Failing GPU

A command failed because the GPU it landed on is busy, out of memory, or in a bad state. Find a GPU that actually works and re-run the command pinned to it.

When to trigger

Any failure whose root cause is the device, not the code. Common signatures:

• CUDA error: out of memory / torch.cuda.OutOfMemoryError
• all CUDA-capable devices are busy or unavailable
• CUDA-capable device(s) is/are busy or unavailable
• RuntimeError: No CUDA GPUs are available
• CUDA error: device-side assert triggered
• A kernel/test that hangs on the first CUDA call

Do not use this for kernel logic bugs, compilation errors, or numerical mismatches — those are not device-health problems.

Procedure

1. Run the scanner:

   bash third_party/tlx/find_working_gpu.sh
   

2. Read the final line, WORKING_GPUS=... (e.g. WORKING_GPUS=0,2,3). These are physical GPU indices.
3. Pick the first working index. If several are free, mention them so the user can parallelize across GPUs.
4. Re-issue the original failing command with CUDA_VISIBLE_DEVICES=<idx>:
   • If the command had no CUDA_VISIBLE_DEVICES, prepend one.
   • If it already set CUDA_VISIBLE_DEVICES, replace that value — do not stack two assignments.

If no GPU works

WORKING_GPUS= is empty. The GPUs may be held by your own stuck processes:

1. Clear them: third_party/tlx/killgpu.sh
2. Re-run bash third_party/tlx/find_working_gpu.sh.
3. If still empty, all GPUs are occupied by other users — report that and stop; there is nothing to switch to.

Command-rewrite examples

# No device set -> prepend
pytest third_party/tlx/tutorials/testing/test_correctness.py
# becomes
CUDA_VISIBLE_DEVICES=2 pytest third_party/tlx/tutorials/testing/test_correctness.py

# Device already set -> replace, don't stack
CUDA_VISIBLE_DEVICES=4 third_party/tlx/denoise.sh python bench.py
# becomes
CUDA_VISIBLE_DEVICES=2 third_party/tlx/denoise.sh python bench.py

Note: denoise.sh defaults to device 4 when CUDA_VISIBLE_DEVICES is unset (third_party/tlx/denoise.sh:6), so always set it explicitly when wrapping a benchmark with denoise.sh after a failure.