The question
The two-GPU path appeared faster until the outputs were inspected. Every image was invalid, so the experiment records a failure and an unresolved sharding suspect rather than promoting the shorter timing.
From the original notebook
Status: BROKEN / DO NOT USE
2026-09-21: the broken PNGs and
.brokenmarker files listed below were deleted at the user’s request; only this record remains.
Source project used to generate these
- Model:
Qwen/Qwen-Image-2.1(Qwen-Image-2.1) - Pipeline:
diffusers.QwenImage21Pipeline - Script:
WORKSPACE/temporary-artifact - Config:
torch_dtype=bfloat16,device_map="balanced"across 2× RTX 3090 - Run:
CUDA_VISIBLE_DEVICES=1,2 conda run -n qwen-image-21 python WORKSPACE/temporary-artifact - Steps/size: 40 steps, 1024×1024, seeds from
random.Random(2026)
Failure
Every image is flat gray noise (no content). The device_map="balanced" sharding of the
diffusers pipeline is the suspect: latents/tensors split across devices, so the denoise loop
never produces a coherent image. Speed was fine (48.1 s, 1.42× vs 68.3 s single-GPU baseline)
but output is invalid — the 2-GPU path is not usable as-is.
Files
| file | md5 (short) | verdict |
|---|---|---|
| qwen21_2gpu_1.png | 53cbc3167ff5 | BROKEN (flat gray noise) |
| qwen21_2gpu_2.png | e4072fe100ea | BROKEN (flat gray noise) |
| qwen21_2gpu_3.png | b5ce06d363dd | BROKEN (flat gray noise) |
| qwen21_2gpu_4.png | 7fe1bed571c0 | BROKEN (flat gray noise) |
| qwen21_2gpu_5.png | 1214027f06ea | BROKEN (flat gray noise) |
Working alternatives (same model): single-GPU bf16 + enable_model_cpu_offload()
(WORKSPACE/temporary-artifact) and fp8 weight-only DiT + offload (WORKSPACE/temporary-artifact).
Keep exploring
Original experiment record. Workstation paths have been generalized. Detailed measurements below retain their original workload and validation boundaries.