[CI/Build] Match perf warmups to benchmark concurrency

Use enough warmup requests to cover a full concurrent batch while preserving the existing two-request minimum.

Signed-off-by: Sy03 <24841857+Sy0307@users.noreply.github.com>

tests/dfx/conftest.py

@@ -653,6 +653,7 @@ def run_benchmark(
     random_input_len: Any | None = None,
     random_output_len: Any | None = None,
     resource_label: str | None = None,
+    num_warmups: int = 2,
 ) -> dict[str, Any]:
     """Run one ``vllm bench serve --omni`` iteration and return parsed metrics.
 
@@ -677,7 +678,7 @@ def run_benchmark(
         + args
         + [
             "--num-warmups",
-            "2",
+            str(num_warmups),
             "--save-result",
             "--result-dir",
             os.environ.get("BENCHMARK_DIR", "tests"),

tests/dfx/perf/scripts/run_benchmark.py

@@ -279,5 +279,6 @@ def test_performance_benchmark(omni_server, benchmark_params):
             random_input_len=params.get("random_input_len"),
             random_output_len=params.get("random_output_len"),
             resource_label=resource_label,
+            num_warmups=max(2, int(concurrency)),
         )
         assert_result(result, params, num_prompt)