tune concurrent test jobs
diff --git a/buildkite/bazelci.py b/buildkite/bazelci.py
index 5b0e388..ded7353 100644
--- a/buildkite/bazelci.py
+++ b/buildkite/bazelci.py
@@ -711,12 +711,11 @@
 
 def concurrent_test_jobs(platform):
     if platform == "windows":
-        return str(multiprocessing.cpu_count() // 4)
+        return "8"
     elif platform == "macos":
-        return str(multiprocessing.cpu_count() // 4)
+        return "12"
     else:
-        return str(multiprocessing.cpu_count() // 3)
-
+        return "12"
 
 def common_flags(bep_file):
     return ["--show_progress_rate_limit=5",