[6/6] mesos git commit: Made `PerfEventSubsystemProcess` can be created without `--perf_events`.

[gi...@apache.org]

Made `PerfEventSubsystemProcess` can be created without `--perf_events`.

If the agent flag `--perf_events` is not specified, the `perf_event`
subsystem (i.e., `PerfEventSubsystemProcess`) can still be created, but
it will not do sampling at all. The reason that we want to do this is,
in some cases, even it is not required to sample any events, we still
want each container to have its own `perf_event` cgroup instead under
the root cgroup.

Review: https://reviews.apache.org/r/67574/


Project: http://git-wip-us.apache.org/repos/asf/mesos/repo
Commit: http://git-wip-us.apache.org/repos/asf/mesos/commit/11f1a7c5
Tree: http://git-wip-us.apache.org/repos/asf/mesos/tree/11f1a7c5
Diff: http://git-wip-us.apache.org/repos/asf/mesos/diff/11f1a7c5

Branch: refs/heads/master
Commit: 11f1a7c509f82076b1bce1a24ccfdf370686aec0
Parents: bb670f1
Author: Qian Zhang <zh...@gmail.com>
Authored: Mon Jun 18 23:23:42 2018 -0700
Committer: Gilbert Song <so...@gmail.com>
Committed: Mon Jun 18 23:36:50 2018 -0700

----------------------------------------------------------------------
 .../isolators/cgroups/subsystems/perf_event.cpp      | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)
----------------------------------------------------------------------


http://git-wip-us.apache.org/repos/asf/mesos/blob/11f1a7c5/src/slave/containerizer/mesos/isolators/cgroups/subsystems/perf_event.cpp
----------------------------------------------------------------------
diff --git a/src/slave/containerizer/mesos/isolators/cgroups/subsystems/perf_event.cpp b/src/slave/containerizer/mesos/isolators/cgroups/subsystems/perf_event.cpp
index 06eca0c..180afc9 100644
--- a/src/slave/containerizer/mesos/isolators/cgroups/subsystems/perf_event.cpp
+++ b/src/slave/containerizer/mesos/isolators/cgroups/subsystems/perf_event.cpp
@@ -44,6 +44,13 @@ Try<Owned<SubsystemProcess>> PerfEventSubsystemProcess::create(
     const Flags& flags,
     const string& hierarchy)
 {
+  // If the agent flag `--perf_events` is not specified, we will not do sampling
+  // at all, so this subsystem is just like a no-op in this case.
+  if (flags.perf_events.isNone()) {
+    return Owned<SubsystemProcess>(
+        new PerfEventSubsystemProcess(flags, hierarchy, set<string>{}));
+  }
+
   if (!perf::supported()) {
     return Error("Perf is not supported");
   }
@@ -54,10 +61,6 @@ Try<Owned<SubsystemProcess>> PerfEventSubsystemProcess::create(
         "interval (" + stringify(flags.perf_interval) + ") is not supported.");
   }
 
-  if (!flags.perf_events.isSome()) {
-    return Error("No perf events specified");
-  }
-
   set<string> events;
   foreach (const string& event,
            strings::tokenize(flags.perf_events.get(), ",")) {
@@ -90,7 +93,9 @@ PerfEventSubsystemProcess::PerfEventSubsystemProcess(
 void PerfEventSubsystemProcess::initialize()
 {
   // Start sampling.
-  sample();
+  if (!events.empty()) {
+    sample();
+  }
 }