Are the test performance results of tests/test_flash_mla.py accurate?

    def flash_mla():

        torch.cuda.synchronize()

        tile_scheduler_metadata, num_splits = get_mla_metadata(cache_seqlens, s_q * h_q // h_kv, h_kv)

I added a `sync()`, and found that the performance was much worse. With `sync()`, it took 360us, while without it, it only took 50us.

Why does it feel like the cost time is a CPU's time? (The kernel submits asynchronously and hasn't finished executing yet.)