vllm - 💡(How to fix) Fix [Performance]: Qwen3.5 with mtp is slower than without [1 participants]

TL;DR

Enabling MTP in Qwen3.5-0.8B may require adjustments to optimize performance, considering the significant difference in throughput metrics with and without MTP.

Guidance

• Review MTP Configuration: Investigate the MTP settings to ensure they are optimized for the current workload, as the performance degradation could be due to suboptimal configuration.
• Analyze Cache Hit Rates: Compare the cache hit rates (Prefix cache hit rate and MM cache hit rate) with and without MTP to understand if cache optimization can improve performance.
• Evaluate SpecDecoding Metrics: Examine the SpecDecoding metrics, such as Mean acceptance length and Per-position acceptance rate, to identify potential bottlenecks in the decoding process that could be affected by MTP.

Example

No specific code snippet can be provided without further details on the MTP implementation or the Qwen3.5-0.8B environment. However, reviewing the loggers.py and metrics.py files, as mentioned in the log outputs, might offer insights into how metrics are collected and potentially where optimizations could be made.

Notes

The provided information suggests a performance regression when MTP is enabled, but without more details on the MTP implementation, the system's hardware, or the specific workload, it's challenging to provide a definitive solution. Further investigation into the system's configuration and the impact of MTP on resource utilization is necessary.

Recommendation

Apply workaround: Given the performance degradation with MTP enabled, it might be necessary to apply workarounds such as adjusting MTP settings, optimizing cache configurations, or revising the decoding process to mitigate the latency increase until a more permanent fix can be implemented.