[Frontend][Misc] Goodput metric support

[Imss27]

This PR adds support of goodput metric for benchmarking serving system.
If the user doesn't specify --goodput, request goodput will not be shown.
Supported service level objectives: TTFT, TPOT, E2EL

FIX #8782

Goodput Context

Goodput is defined as the number of completed requests per second that meet certain Service Level Objectives, such as TTFT, TPOT, E2E Latency which could be defined by the users.

Goodput aims to benchmark GenAI services from a user’s perspective and will provide insights for service providers to further optimize their serving and inference system for better User Experience.

Why do we need Goodput?

1. Users tolerate latency(TTFT, TPOT, E2E Latency) differently for different applications.

2. High throughput does not mean high goodput

Usage Example

Start a server

vllm serve meta-llama/Llama-3.2-1B-Instruct \
    --disable-log-requests \
    --tensor-parallel-size 1 \

Benchmark serving with goodput

cd benchmarks
python benchmark_serving.py \
    --backend vllm \
    --model meta-llama/Llama-3.2-1B-Instruct \
    --dataset-name sonnet \
    --num-prompt=10 \
    --dataset-path="sonnet.txt" \
    --sonnet-input-len 600 \
    --save-result  \
    --goodput ttft:500 tpot:14 e2el:2500

Example Console Output

============ Serving Benchmark Result ============
Successful requests:                     10        
Benchmark duration (s):                  2.37      
Total input tokens:                      5477      
Total generated tokens:                  1500      
Request throughput (req/s):              4.23      
Request goodput (req/s):                 1.69      
Output token throughput (tok/s):         634.23    
Total Token throughput (tok/s):          2950.01   
---------------Time to First Token----------------
Mean TTFT (ms):                          288.13    
Median TTFT (ms):                        272.04    
P99 TTFT (ms):                           435.43    
-----Time per Output Token (excl. 1st token)------
Mean TPOT (ms):                          13.93     
Median TPOT (ms):                        14.04     
P99 TPOT (ms):                           14.89     
---------------Inter-token Latency----------------
Mean ITL (ms):                           13.93     
Median ITL (ms):                         12.85     
P99 ITL (ms):                            14.35     
==================================================

TODO

• Investigate proper service level objectives for CI Dashboard model.
• Add goodput plot to CI Dashboard.

cc: @ywang96 @KuntaiDu Any inputs from you and the community will be extremely valuable for future CI Dashboard work on Goodput. Like what kind of plots, setting what kind of SLOs for different LLM applications on different CI hardware.

---

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[andoorve]

Hey @ywang96 @KuntaiDu do you have any thoughts on @Imss27 question above?

cc: @ywang96 @KuntaiDu Any inputs from you and the community will be extremely valuable for future CI Dashboard work on Goodput. Like what kind of plots, setting what kind of SLOs for different LLM applications on different CI hardware.

[KuntaiDu]

I am not an industry guy so I am not the best guy checking if the definition of TTFT < TTFT SLO and Average TPOT < TPOT SLO is the right way to define goodput (especially using average TPOT < TPOT SLO to define goodput) @comaniac @ywang96 would be great if you can share your thoughts!

[comaniac]

Better to provide the paper link given that not many people know goodput atm.

[comaniac]

Suggested change

	if slo_name not in VALID_NAMES:
	raise ValueError(
	f"Invalid metric name found, {slo_name}: {slo_val}. "
	f"The service level objective name should be one of "
	f"\"ttft\", \"tpot\", \"e2el\". ")
	if slo_name not in VALID_NAMES:
	raise ValueError(
	f"Invalid metric name found, {slo_name}: {slo_val}. "
	"The service level objective name should be one of "
	f"{str(VALID_NAMES)}.")

[comaniac]

No need to add f if there's no variables.

[comaniac]

The name slos_dict is confusing in this script. Maybe call it gootput_config_dict or slo_config_dict. I'll prefer to have goodput in the name because the purpose of this config is only for calculating goodput.

[comaniac]

Make this as a global variable and rename it to be more clear.

[comaniac]

I am not an industry guy so I am not the best guy checking if the definition of TTFT < TTFT SLO and Average TPOT < TPOT SLO is the right way to define goodput (especially using average TPOT < TPOT SLO to define goodput) @comaniac @ywang96 would be great if you can share your thoughts!

Goodput is a well-defined term in https://arxiv.org/pdf/2401.09670. @Imss27 please provide more information about goodput in the RFC, PR description and the script.

[GindaChen]

I am not an industry guy so I am not the best guy checking if the definition of TTFT < TTFT SLO and Average TPOT < TPOT SLO is the right way to define goodput (especially using average TPOT < TPOT SLO to define goodput) @comaniac @ywang96 would be great if you can share your thoughts!

Yes - I can confirm that in our paper, a request is "good" if

• its TTFT < TTFT SLO
• its average TPOT < TPOT SLO

In practice, whether this is a good enough metric remains questionable, although this is what a lot of other LLM system paper still continues to use.

[Imss27]

Thanks for the review and discussion! Updated according to the great suggestions.

@comaniac Please take a look when you get a chance😄

[comaniac]

Otherwise LGTM

[comaniac]

The current implementation needs to manually add more metrics as needed. Can make this logic more flexible? For example I may want to use P90 e2e latency as the SLO later.

[Imss27]

This is indeed a problem for future possible new request-level metric. A possible implementation to be more extensible would require much more refactoring and should be a separate PR. We would need to decouple request-level Metrics and the computation process of output into different classes. In this way, I think whenever a new metric is defined in new request-level Metrics class, we can easily support to use it as an SLO for goodput computation.

But for the P90 e2e latency, I think we don't need to worry about it.

The goodput we defined is a request-level metric. We can only consider P90 e2e latency based on all requests' information. And if the SLO only contains e2e latency constraint and we set it to P90 e2e latency value, it basically means we want the goodput ≈ throughput * 90%. But SLOs should be set based on LLM applications, and the SLO values should be something that bring good user experience

[comaniac]

Make sense. So I could use e2e latency as the SLO and check if gootput >= 0.9 * throughput to see if my P90 latency requirement is met.

[comaniac]

Suggested change

	req_metric_list = list(zip(*valid_metrics))
	for req_metric in req_metric_list:
	for req_metric in zip(*valid_metrics):

[comaniac]

Suggested change

	is_good_req = True
	for i in range(len(slo_values)):
	if slo_values[i] < req_metric[i]:
	is_good_req = False
	break
	is_good_req = all([s < r for s, r in zip(slo_values, req_metric)])

[Imss27]

Thanks! Updated according to all suggestions here.😄

[Imss27]

Found a bug during local test🤣, we should compare values in the opposite direction if using all() for SLOs and req_metrics. Please take a look when you get a chance. @comaniac