Add an option to launch cacheflow without ray

[zhuohan123]

Fix #23

[WoosukKwon]

Thanks for the PR. Left some comments. BTW, could you show the latency benchmarks before and after this PR?

[zhuohan123]

Latency with Ray:

ubuntu@ray-zhuohan-cf-head-6dd317a2-compute:~/nfs/cacheflow/cacheflow/benchmark$ python benchmark_latency.py --model facebook/opt-13b --use-ray
Namespace(batch_size=8, block_size=16, dtype='half', input_len=32, max_num_batched_tokens=2560, max_num_sequences=256, model='facebook/opt-13b', model_path='~/.cacheflow/model_weights', n=1, output_len=128, pipeline_parallel_size=1, seed=0, swap_space=20, tensor_parallel_size=1, use_beam_search=False, use_dummy_weights=False, use_ray=True)
2023-04-29 16:28:04,226 INFO worker.py:1622 -- Started a local Ray instance. View the dashboard at http://127.0.0.1:8265
# GPU blocks: 987, # CPU blocks: 1638
SamplingParams(n=1, temperature=1.0, top_p=1.0, use_beam_search=False, stop_token_ids=set(), max_num_steps=128, num_logprobs=0, context_window_size=None)
Warm up step
Profile step: 100%|██████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████| 3/3 [00:10<00:00,  3.55s/it]
Avg latency: 3.54734468460083 seconds

Latency without Ray:

ubuntu@ray-zhuohan-cf-head-6dd317a2-compute:~/nfs/cacheflow/cacheflow/benchmark$ python benchmark_latency.py --model facebook/opt-13b
Namespace(batch_size=8, block_size=16, dtype='half', input_len=32, max_num_batched_tokens=2560, max_num_sequences=256, model='facebook/opt-13b', model_path='~/.cacheflow/model_weights', n=1, output_len=128, pipeline_parallel_size=1, seed=0, swap_space=20, tensor_parallel_size=1, use_beam_search=False, use_dummy_weights=False, use_ray=False)
# GPU blocks: 987, # CPU blocks: 1638
SamplingParams(n=1, temperature=1.0, top_p=1.0, use_beam_search=False, stop_token_ids=set(), max_num_steps=128, num_logprobs=0, context_window_size=None)
Warm up step
Profile step: 100%|██████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████| 3/3 [00:09<00:00,  3.32s/it]
Avg latency: 3.3214046160380044 seconds

[WoosukKwon]

Thanks!