mesos git commit: Improved performance of cgroups::read by verifying after failure.

[bm...@apache.org]

Repository: mesos
Updated Branches:
  refs/heads/master d0c7d8993 -> 0ad92e2d9


Improved performance of cgroups::read by verifying after failure.

It turns out that cgroups::verify is expensive and leads to a severe
performance issue on the agent during container metrics collection
if there are a lot of containers on the agent. See MESOS-8418.

Since cgroups::verify serves to provide a helpful error message,
this patch preserves the error message, but only if the read fails.

Longer term, there probably needs to be some re-structuring of the
code to make verification caller-controlled, or perhaps the verify
code can occur consistently post-operation (as done in this patch),
or perhaps verify can be optimized substantially.

Review: https://reviews.apache.org/r/67923/


Project: http://git-wip-us.apache.org/repos/asf/mesos/repo
Commit: http://git-wip-us.apache.org/repos/asf/mesos/commit/0ad92e2d
Tree: http://git-wip-us.apache.org/repos/asf/mesos/tree/0ad92e2d
Diff: http://git-wip-us.apache.org/repos/asf/mesos/diff/0ad92e2d

Branch: refs/heads/master
Commit: 0ad92e2d9e2152699ead84739e86f92edd1b462e
Parents: d0c7d89
Author: Benjamin Mahler <bm...@apache.org>
Authored: Mon Jul 16 17:22:45 2018 -0700
Committer: Benjamin Mahler <bm...@apache.org>
Committed: Mon Jul 16 17:25:12 2018 -0700

----------------------------------------------------------------------
 src/linux/cgroups.cpp | 21 +++++++++++++++++----
 1 file changed, 17 insertions(+), 4 deletions(-)
----------------------------------------------------------------------


http://git-wip-us.apache.org/repos/asf/mesos/blob/0ad92e2d/src/linux/cgroups.cpp
----------------------------------------------------------------------
diff --git a/src/linux/cgroups.cpp b/src/linux/cgroups.cpp
index b12e63c..5c96484 100644
--- a/src/linux/cgroups.cpp
+++ b/src/linux/cgroups.cpp
@@ -917,12 +917,25 @@ Try<string> read(
     const string& cgroup,
     const string& control)
 {
-  Option<Error> error = verify(hierarchy, cgroup, control);
-  if (error.isSome()) {
-    return error.get();
+  Try<string> read = internal::read(hierarchy, cgroup, control);
+
+  // It turns out that `verify()` is expensive, so rather than
+  // verifying *prior* to the read, as is currently done for other
+  // cgroup helpers, we only verify if the read fails. This ensures
+  // we still provide a good error message. See: MESOS-8418.
+  //
+  // TODO(bmahler): Longer term, verification should be done
+  // explicitly by the caller, or its performance should be
+  // improved, or verification could be done consistently
+  // post-failure, as done here.
+  if (read.isError()) {
+    Option<Error> error = verify(hierarchy, cgroup, control);
+    if (error.isSome()) {
+      return error.get();
+    }
   }
 
-  return internal::read(hierarchy, cgroup, control);
+  return read;
 }