Vllm 0.23.0 fp8_e4m3 doesn't work on H200s

#10
by tkg61 - opened

VLLM returns an error when using fp8_e4m3 for kv-cache type. Have to use "fp8" instead.

Command: vllm serve zai-org/GLM-5.2-FP8 --trust-remote-code --tensor-parallel-size 8 --tool-call-parser glm47 --enable
-auto-tool-choice --reasoning-parser glm45 --served-model-name zai-org/GLM-5.2-FP8 --kv-cache-dtype fp8_e4m3 --gpu-memory-utilization 0.95

Error:
ValueError: No valid attention backend found for cuda with AttentionSelectorConfig(head_size=576, dtype=torch.bfloat16, kv_cache_dtype=fp8_e4m3, block_size=None, use
_mla=True, has_sink=False, use_sparse=True, use_mm_prefix=False, use_per_head_quant_scales=False, attn_type=AttentionType.DECODER, use_non_causal=False, use_batch_invariant=False, use_kv_connector=False). Reasons: {FLASH_ATTN_MLA: [kv_ca
che_dtype not supported, sparse not supported], FLASHMLA: [sparse not supported], FLASHINFER_MLA: [sparse not supported, compute capability not supported], TRITON_MLA: [sparse not supported], FLASHMLA_SPARSE: [kv_cache_dtype not supporte
d]}.

Also, H200s don't support a 1M context window unless that has something to do with using fp8 kv-cache. Could someone update the docs for H200s specifically?

@tkg61 you need B200's for 1M context. It is stated in the recipe guide here: https://recipes.vllm.ai/zai-org/GLM-5.2

For the H200's, you need 8 of them and context length of 512k.

@tkg61 in H200, we recommend to use --kv-cache-dtype fp8_ds_mla for fp8 kv cache. and try to reduce concurrency like --max-num-seqs 32
thanks for your understanding

ZHANGYUXUAN-zR changed discussion status to closed

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