From: Jason Dillaman <dillaman@redhat.com>
Date: Fri, 20 Oct 2017 02:24:31 +0000 (-0400)
Subject: osdc/Objecter: skip sparse-read result decode if bufferlist is empty
X-Git-Tag: v13.0.1~474^2
X-Git-Url: http://git-server-git.apps.pok.os.sepia.ceph.com/?a=commitdiff_plain;h=refs%2Fpull%2F18400%2Fhead;p=ceph.git

osdc/Objecter: skip sparse-read result decode if bufferlist is empty

If the OSD does not execute sub-ops due to errors encountered prior to
the sub-op, the sub-op result remains zeroed with empty out data.
Attempting to decode the empty bufferlist results in large exception
handling CPU overhead.

Fixes: http://tracker.ceph.com/issues/21844
Signed-off-by: Jason Dillaman <dillaman@redhat.com>
---

diff --git a/src/osdc/Objecter.h b/src/osdc/Objecter.h
index 3358d6bb24e8c..569e328ee6c4e 100644
--- a/src/osdc/Objecter.h
+++ b/src/osdc/Objecter.h
@@ -335,13 +335,20 @@ struct ObjectOperation {
     void finish(int r) override {
       bufferlist::iterator iter = bl.begin();
       if (r >= 0) {
-	try {
-	  ::decode(*extents, iter);
-	  ::decode(*data_bl, iter);
-	} catch (buffer::error& e) {
-	  if (prval)
-	    *prval = -EIO;
-	}
+        // NOTE: it's possible the sub-op has not been executed but the result
+        // code remains zeroed. Avoid the costly exception handling on a
+        // potential IO path.
+        if (bl.length() > 0) {
+	  try {
+	    ::decode(*extents, iter);
+	    ::decode(*data_bl, iter);
+	  } catch (buffer::error& e) {
+	    if (prval)
+              *prval = -EIO;
+	  }
+        } else if (prval) {
+          *prval = -EIO;
+        }
       }
     }
   };