Support CPU profiling in mongod.

Add commands _cpuProfileStart and _cpuProfileStop to allow you to selectively
enable and disable profiling, around the regions of execution that interest you.

SConstruct

@@ -190,6 +190,9 @@ for shortName in getThirdPartyShortNames():
 
 add_option( "use-system-all" , "use all system libraries " + shortName , 0 , True )
 
+add_option( "use-cpu-profiler",
+            "Link against the google-perftools profiler library",
+            0, True )
 
 # don't run configure if user calls --help
 if GetOption('help'):
@@ -1163,6 +1166,10 @@ def checkErrorCodes():
 
 checkErrorCodes()
 
+if has_option( 'use-cpu-profiler' ):
+    coreServerFiles.append( 'src/mongo/db/commands/cpuprofile.cpp' )
+    env.Append( LIBS=['profiler'] )
+
 # main db target
 mongod = env.Program( "mongod" , commonFiles + coreDbFiles + coreServerFiles + serverOnlyFiles + mongodOnlyFiles )
 Default( mongod )

src/mongo/db/commands/cpuprofile.cpp

@@ -0,0 +1,112 @@
+// @file cpuprofile.cpp
+
+/**
+ * This module provides commands for starting and stopping the Google perftools
+ * cpu profiler linked into mongod.
+ *
+ * The following command enables the not-currently-enabled profiler, and writes
+ * the profile data to the specified "profileFilename."
+ *     { _cpuProfilerStart: { profileFilename: '/path/on/mongod-host.prof' } }
+ *
+ * The following command disables the already-enabled profiler:
+ *     { _cpuProfilerStop: 1}
+ *
+ * The commands defined here, and profiling, are only available when enabled at
+ * build-time with the "--use-cpu-profiler" argument to scons.
+ *
+ * Example SCons command line, assuming you've installed google-perftools in
+ * /usr/local:
+ *
+ *     scons --release --use-cpu-profiler \
+ *         --cpppath=/usr/local/include --libpath=/usr/loca/lib
+ */
+
+#include "google/profiler.h"
+#include "mongo/db/commands.h"
+
+namespace mongo {
+
+    namespace {
+
+        /**
+         * Common code for the implementation of cpu profiler commands.
+         */
+        class CpuProfilerCommand : public Command {
+        public:
+            CpuProfilerCommand( char const *name ) : Command( name ) {}
+            virtual bool slaveOk() const { return true; }
+            virtual bool adminOnly() const { return true; }
+            virtual bool localHostOnlyIfNoAuth() const { return true; }
+
+            // This is an abuse of the global dbmutex.  We only really need to
+            // ensure that only one cpuprofiler command runs at once; it would
+            // be fine for it to run concurrently with other operations.
+            virtual LockType locktype() const { return WRITE; }
+        };
+
+        /**
+         * Class providing implementation of the _cpuProfilerStart command.
+         */
+        class CpuProfilerStartCommand : public CpuProfilerCommand {
+        public:
+            CpuProfilerStartCommand() : CpuProfilerCommand( commandName ) {}
+
+            virtual bool run( string const &db,
+                              BSONObj &cmdObj,
+                              int options,
+                              string &errmsg,
+                              BSONObjBuilder &result,
+                              bool fromRepl );
+
+            static char const *const commandName;
+        } cpuProfilerStartCommandInstance;
+
+        /**
+         * Class providing implementation of the _cpuProfilerStop command.
+         */
+        class CpuProfilerStopCommand : public CpuProfilerCommand {
+        public:
+            CpuProfilerStopCommand() : CpuProfilerCommand( commandName ) {}
+
+            virtual bool run( string const &db,
+                              BSONObj &cmdObj,
+                              int options,
+                              string &errmsg,
+                              BSONObjBuilder &result,
+                              bool fromRepl );
+
+            static char const *const commandName;
+        } cpuProfilerStopCommandInstance;
+
+        char const *const CpuProfilerStartCommand::commandName = "_cpuProfilerStart";
+        char const *const CpuProfilerStopCommand::commandName = "_cpuProfilerStop";
+
+        bool CpuProfilerStartCommand::run( string const &db,
+                                           BSONObj &cmdObj,
+                                           int options,
+                                           string &errmsg,
+                                           BSONObjBuilder &result,
+                                           bool fromRepl ) {
+
+            std::string profileFilename = cmdObj[commandName]["profileFilename"].String();
+            if ( ! ::ProfilerStart( profileFilename.c_str() ) ) {
+                errmsg = "Failed to start profiler";
+                return false;
+            }
+            return true;
+        }
+
+        bool CpuProfilerStopCommand::run( string const &db,
+                                          BSONObj &cmdObj,
+                                          int options,
+                                          string &errmsg,
+                                          BSONObjBuilder &result,
+                                          bool fromRepl ) {
+            ::ProfilerStop();
+            return true;
+        }
+
+    }  // namespace
+
+}  // namespace mongo
+