timer: pick a single unit based on max duration.

lib/spack/llnl/util/lang.py

@@ -741,6 +741,18 @@ def _n_xxx_ago(x):
     raise ValueError(msg)
 
 
+def pretty_seconds_formatter(seconds):
+    if seconds >= 1:
+        multiplier, unit = 1, "s"
+    elif seconds >= 1e-3:
+        multiplier, unit = 1e3, "ms"
+    elif seconds >= 1e-6:
+        multiplier, unit = 1e6, "us"
+    else:
+        multiplier, unit = 1e9, "ns"
+    return lambda s: "%.3f%s" % (multiplier * s, unit)
+
+
 def pretty_seconds(seconds):
     """Seconds to string with appropriate units
 
@@ -750,15 +762,7 @@ def pretty_seconds(seconds):
     Returns:
         str: Time string with units
     """
-    if seconds >= 1:
-        value, unit = seconds, "s"
-    elif seconds >= 1e-3:
-        value, unit = seconds * 1e3, "ms"
-    elif seconds >= 1e-6:
-        value, unit = seconds * 1e6, "us"
-    else:
-        value, unit = seconds * 1e9, "ns"
-    return "%.3f%s" % (value, unit)
+    return pretty_seconds_formatter(seconds)(seconds)
 
 
 class RequiredAttributeError(ValueError):

lib/spack/spack/test/util/timer.py

@@ -120,9 +120,9 @@ def test_timer_write():
 
     output = text_buffer.getvalue().splitlines()
     assert "timer" in output[0]
-    assert "1.0000s" in output[0]
+    assert "1.000s" in output[0]
     assert "total" in output[1]
-    assert "3.0000s" in output[1]
+    assert "3.000s" in output[1]
 
     deserialized = json.loads(json_buffer.getvalue())
     assert deserialized == {

lib/spack/spack/util/timer.py

@@ -14,7 +14,7 @@
 from collections import OrderedDict, namedtuple
 from contextlib import contextmanager
 
-from llnl.util.lang import pretty_seconds
+from llnl.util.lang import pretty_seconds_formatter
 
 import spack.util.spack_json as sjson
 
@@ -139,12 +139,16 @@ def write_json(self, out=sys.stdout):
 
     def write_tty(self, out=sys.stdout):
         """Write a human-readable summary of timings"""
-        # Individual timers ordered by registration
-        formatted = [(p, f"{self.duration(p):.4f}s") for p in self.phases]
 
-        # Total time
-        formatted.append(("total", f"{self.duration():.4f}s"))
+        times = [self.duration(p) for p in self.phases]
+
+        # Get a consistent unit for the time
+        pretty_seconds = pretty_seconds_formatter(max(times))
+
+        # Tuples of (phase, time) including total.
+        formatted = list(zip(self.phases, times))
+        formatted.append(("total", self.duration()))
 
         # Write to out
         for name, duration in formatted:
-            out.write(f"    {name:10s} {duration:>10s}\n")
+            out.write(f"    {name:10s} {pretty_seconds(duration):>10s}\n")