address comments

tools/run_tests/python_utils/jobset.py

@@ -201,6 +201,7 @@ class JobSpec(object):
         self.verbose_success = verbose_success
         self.logfilename = logfilename
         if self.logfilename and self.flake_retries != 0 and self.timeout_retries != 0:
+            # Forbidden to avoid overwriting the test log when retrying.
             raise Exception(
                 'Cannot use custom logfile when retries are enabled')
 

tools/run_tests/run_tests_matrix.py

@@ -56,8 +56,9 @@ def _report_filename(name):
 
 
 def _report_logfilename(name):
-    """Generates report file name with directory structure that leads to better presentation by internal CI"""
+    """Generates log file name that corresponds to name generated by _report_filename"""
-    # 'sponge_log.log' suffix must be there for test log to get recognized by kokoro.
+    # 'sponge_log.log' suffix must be there for log to get recognized as "target log"
+    # for the corresponding 'sponge_log.xml' report.
     return '%s/%s' % (_safe_report_name(name), 'sponge_log.log')