Build retrieval improvements (#4412)

### Motivation

Small changes for the build retrieval metric, as requested per Chrome
folks after initially using the feature:

* Adding the time for listing fuzz targets as a step
* Added the total retrieval duration
* Tracking metric as minutes, for readability

Part of #4271

src/clusterfuzz/_internal/build_management/build_manager.py

@@ -299,6 +299,17 @@ def set_env_var(name, value):
     logs.error(f'Could not find app {app_name!r} in search directories.')
 
 
+def _emit_job_build_retrieval_metric(start_time, step, build_type):
+  elapsed_minutes = (time.time() - start_time) / 60
+  monitoring_metrics.JOB_BUILD_RETRIEVAL_TIME.add(
+      elapsed_minutes, {
+          'job': os.getenv('JOB_NAME'),
+          'platform': environment.platform(),
+          'step': step,
+          'build_type': build_type,
+      })
+
+
 class BaseBuild:
   """Represents a build."""
 
@@ -440,14 +451,7 @@ def _download_and_open_build_archive(self, base_build_dir: str,
     try:
       start_time = time.time()
       storage.copy_file_from(build_url, build_local_archive)
-      build_download_duration = time.time() - start_time
-      monitoring_metrics.JOB_BUILD_RETRIEVAL_TIME.add(
-          build_download_duration, {
-              'job': os.getenv('JOB_NAME'),
-              'platform': environment.platform(),
-              'step': 'download',
-              'build_type': self._build_type,
-          })
+      _emit_job_build_retrieval_metric(start_time, 'download', self._build_type)
     except Exception as e:
       logs.error(f'Unable to download build from {build_url}: {e}')
       raise
@@ -522,7 +526,11 @@ def _unpack_build(self,
         if not self._unpack_everything:
           # We will never unpack the full build so we need to get the targets
           # from the build archive.
+          list_fuzz_target_start_time = time.time()
           self._fuzz_targets = list(build.list_fuzz_targets())
+          _emit_job_build_retrieval_metric(list_fuzz_target_start_time,
+                                           'list_fuzz_targets',
+                                           self._build_type)
           # We only want to unpack a single fuzz target if unpack_everything is
           # False.
           fuzz_target_to_unpack = self.fuzz_target
@@ -547,15 +555,8 @@ def _unpack_build(self,
             fuzz_target=fuzz_target_to_unpack,
             trusted=trusted)
 
-        unpack_elapsed_time = time.time() - unpack_start_time
-
-        monitoring_metrics.JOB_BUILD_RETRIEVAL_TIME.add(
-            unpack_elapsed_time, {
-                'job': os.getenv('JOB_NAME'),
-                'platform': environment.platform(),
-                'step': 'unpack',
-                'build_type': self._build_type,
-            })
+        _emit_job_build_retrieval_metric(unpack_start_time, 'unpack',
+                                         self._build_type)
 
     except Exception as e:
       logs.error(f'Unable to unpack build archive {build_url}: {e}')
@@ -567,6 +568,7 @@ def _unpack_build(self,
       partial_build_file_path = os.path.join(build_dir, PARTIAL_BUILD_FILE)
       utils.write_data_to_file('', partial_build_file_path)
 
+    _emit_job_build_retrieval_metric(start_time, 'total', self._build_type)
     elapsed_time = time.time() - start_time
 
     elapsed_mins = elapsed_time / 60.
@@ -598,7 +600,10 @@ def fuzz_targets(self):
     if not self._fuzz_targets and self._unpack_everything:
       # we can lazily compute that when unpacking the whole archive, since we
       # know all the fuzzers will be in the build directory.
+      start_time = time.time()
       self._fuzz_targets = list(self._get_fuzz_targets_from_dir(self.build_dir))
+      _emit_job_build_retrieval_metric(start_time, 'list_fuzz_targets',
+                                       self._build_type)
     return self._fuzz_targets
 
   def exists(self):
@@ -905,15 +910,8 @@ def _unpack_custom_build(self):
                                      build_local_archive):
       return False
 
-    build_download_time = time.time() - download_start_time
-    monitoring_metrics.JOB_BUILD_RETRIEVAL_TIME.add(
-        build_download_time, {
-            'job': os.getenv('JOB_NAME'),
-            'platform': environment.platform(),
-            'step': 'download',
-            'build_type': self._build_type,
-        })
-
+    _emit_job_build_retrieval_metric(download_start_time, 'download',
+                                     self._build_type)
     # If custom binary is an archive, then unpack it.
     if archive.is_archive(self.custom_binary_filename):
       try:
@@ -933,14 +931,8 @@ def _unpack_custom_build(self):
         # Unpack belongs to the BuildArchive class
         unpack_start_time = time.time()
         build.unpack(self.build_dir, trusted=True)
-        build_unpack_time = time.time() - unpack_start_time
-        monitoring_metrics.JOB_BUILD_RETRIEVAL_TIME.add(
-            build_unpack_time, {
-                'job': os.getenv('JOB_NAME'),
-                'platform': environment.platform(),
-                'step': 'unpack',
-                'build_type': self._build_type,
-            })
+        _emit_job_build_retrieval_metric(unpack_start_time, 'unpack',
+                                         self._build_type)
       except:
         build.close()
         logs.error('Unable to unpack build archive %s.' % build_local_archive)
@@ -949,6 +941,9 @@ def _unpack_custom_build(self):
       build.close()
       # Remove the archive.
       shell.remove_file(build_local_archive)
+
+    _emit_job_build_retrieval_metric(download_start_time, 'download',
+                                     self._build_type)
     return True
 
   def setup(self):

src/clusterfuzz/_internal/metrics/monitoring_metrics.py

@@ -48,7 +48,7 @@
     'task/build_retrieval_time',
     bucketer=monitor.FixedWidthBucketer(width=0.05, num_finite_buckets=20),
     description=('Distribution of fuzz task\'s build retrieval times. '
-                 '(grouped by fuzzer/job)'),
+                 '(grouped by fuzzer/job, in minutes).'),
     field_spec=[
         monitor.StringField('job'),
         monitor.StringField('step'),