Mac: Fix %cpu in task manager.

base/process_util_mac.mm

 // Copyright (c) 2008 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 
 #include "base/process_util.h"
 
 #import <Cocoa/Cocoa.h>
 #include <crt_externs.h>
 #include <mach/mach.h>
@@ skipping 237 matching lines @@
   (r)->tv_usec = (a)->microseconds;       \
 } while (0)
 
 double ProcessMetrics::GetCPUUsage() {
   mach_port_t task = TaskForPid(process_);
   if (task == MACH_PORT_NULL)
     return 0;
 
   kern_return_t kr;
 
-  // TODO(thakis): Libtop doesn't use thread info. How can they get away
-  // without it?
+  // Libtop explicitly loops over the threads (libtop_pinfo_update_cpu_usage()
+  // in libtop.c), but this is more concise and gives the same results:
   task_thread_times_info thread_info_data;
   mach_msg_type_number_t thread_info_count = TASK_THREAD_TIMES_INFO_COUNT;
   kr = task_info(task,
                  TASK_THREAD_TIMES_INFO,
                  reinterpret_cast<task_info_t>(&thread_info_data),
                  &thread_info_count);
   if (kr != KERN_SUCCESS) {
     // Most likely cause: |task| is a zombie.
     return 0;
   }
@@ skipping 30 matching lines @@
     return 0;
   }
 
   int64 system_time_delta = task_time - last_system_time_;
   int64 time_delta = time - last_time_;
   DCHECK(time_delta != 0);
   if (time_delta == 0)
     return 0;
 
   // We add time_delta / 2 so the result is rounded.
-  double cpu = static_cast<double>(
-      (system_time_delta * 100.0 + time_delta / 2.0) / time_delta);
+  double cpu = static_cast<double>((system_time_delta * 100.0) / time_delta);
 
   last_system_time_ = task_time;
   last_time_ = time;
 
   return cpu;
 }
 
 mach_port_t ProcessMetrics::TaskForPid(ProcessHandle process) const {
   mach_port_t task = MACH_PORT_NULL;
   if (port_provider_)
@@ skipping 110 matching lines @@
   CHECK(g_old_malloc && g_old_calloc && g_old_valloc && g_old_realloc)
       << "Failed to get system allocation functions.";
 
   default_zone->malloc = oom_killer_malloc;
   default_zone->calloc = oom_killer_calloc;
   default_zone->valloc = oom_killer_valloc;
   default_zone->realloc = oom_killer_realloc;
 }
 
 }  // namespace base