Exclude noisy benchmarks from labelling computations (#29039)

* Exclude noisy benchmarks from labelling computations

* Automated change: Fix sanity tests

Co-authored-by: ctiller <ctiller@users.noreply.github.com>

tools/profiling/microbenchmarks/bm_diff/bm_diff.py

@@ -214,7 +214,11 @@ def diff(bms, loops, regex, track, old, new, counters):
     # figure out the significance of the changes... right now we take the 95%-ile
     # benchmark delta %-age, and then apply some hand chosen thresholds
     histogram = []
-    for bm in benchmarks.values():
+    _NOISY = ["BM_WellFlushed"]
+    for name, bm in benchmarks.items():
+        if name in _NOISY:
+            print("skipping noisy benchmark '%s' for labelling evaluation" %
+                  name)
         if bm.skip():
             continue
         d = bm.speedup['cpu_time']