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Commit 436d04ed authored by Narayan Kamath's avatar Narayan Kamath
Browse files

ActivityManagerService: Rework dumping of top CPU processes. 

Try and measure the CPU load as early as possible to get a more
realistic picture. Also, reduce the sampling set for the CPU
load to a 200ms timeslice.

Pros:
- Stack dumping for the first / native processes can take a while,
  which might mean that our CPU measurement happens several seconds
  after the ANR occurred.
- CPU measurements might be skewed by the stack dumping itself.

Cons:
- We capture traces for the "important" processes ~500ms later. This
  will not make any difference to the class of ANRs caused by
  deadlocks etc. It might however mean that we get unhelpful stack
  traces for ANRs caused by starvation / livelock etc. since the main
  thread might have made progress in this additional time. Arguably,
  this is isn't a big drawback since ANR reports from such apps are
  likely to be noisy anyway.

Bug: 32064548
Test: Manual: Compared two ProcessCpuTrackers that would fire at the
      same time, one with a 500ms timeslice and another with a 200ms
      timeslice. There was usually no difference in the top 5
      processes in their working sets. When there was, it was just an
      ordering difference the vast majority of the time.

Change-Id: Ic81802cb62828fdc02a01b229dc1d6545a465ecd
parent 4eeb7b35

services/core/java/com/android/server/am/ActivityManagerService.java

+43 −38
Original line number Diff line number Diff line
@@ -5399,7 +5399,35 @@ public class ActivityManagerService extends IActivityManager.Stub 
            return null;

        }













        dumpStackTraces(tracesPath, firstPids, processCpuTracker, lastPids, nativePids);













        ArrayList<Integer> extraPids = null;

























        // Lastly, measure CPU usage.













        if (processCpuTracker != null) {













            processCpuTracker.init();













            try {













                Thread.sleep(200);













            } catch (InterruptedException ignored) {













            }

























            processCpuTracker.update();

























            // We'll take the stack crawls of just the top apps using CPU.













            final int N = processCpuTracker.countWorkingStats();













            extraPids = new ArrayList<>();













            for (int i = 0; i < N && extraPids.size() < 5; i++) {













                ProcessCpuTracker.Stats stats = processCpuTracker.getWorkingStats(i);













                if (lastPids.indexOfKey(stats.pid) >= 0) {













                    if (DEBUG_ANR) Slog.d(TAG, "Collecting stacks for extra pid " + stats.pid);

























                    extraPids.add(stats.pid);













                } else if (DEBUG_ANR) {













                    Slog.d(TAG, "Skipping next CPU consuming process, not a java proc: "













                            + stats.pid);













                }













            }













        }

























        dumpStackTraces(tracesPath, firstPids, nativePids, extraPids);















        return tracesFile;















    }
























@@ -5461,8 +5489,7 @@ public class ActivityManagerService extends IActivityManager.Stub













    }





























    private static void dumpStackTraces(String tracesPath, ArrayList<Integer> firstPids,













            ProcessCpuTracker processCpuTracker, SparseArray<Boolean> lastPids,













            ArrayList<Integer> nativePids) {













            ArrayList<Integer> nativePids, ArrayList<Integer> extraPids) {















        // Use a FileObserver to detect when traces finish writing.















        // The order of traces is considered important to maintain for legibility.















        DumpStackFileObserver observer = new DumpStackFileObserver(tracesPath);










@@ -5518,43 +5545,21 @@ public class ActivityManagerService extends IActivityManager.Stub













                }















            }



























            // Lastly, measure CPU usage.













            if (processCpuTracker != null) {













                processCpuTracker.init();













                System.gc();













                processCpuTracker.update();













                try {













                    synchronized (processCpuTracker) {













                        processCpuTracker.wait(500); // measure over 1/2 second.













                    }













                } catch (InterruptedException e) {













                }













                processCpuTracker.update();

























                // We'll take the stack crawls of just the top apps using CPU.













                final int N = processCpuTracker.countWorkingStats();













                int numProcs = 0;













                for (int i=0; i<N && numProcs<5; i++) {













                    ProcessCpuTracker.Stats stats = processCpuTracker.getWorkingStats(i);













                    if (lastPids.indexOfKey(stats.pid) >= 0) {













                        numProcs++;













            // Lastly, dump stacks for all extra PIDs from the CPU tracker.













            if (extraPids != null) {













                for (int pid : extraPids) {













                    if (DEBUG_ANR) Slog.d(TAG, "Collecting stacks for extra pid " + pid);



























                        if (DEBUG_ANR) Slog.d(TAG, "Collecting stacks for extra pid " + stats.pid);

























                        final long timeTaken = observer.dumpWithTimeout(stats.pid, remainingTime);













                    final long timeTaken = observer.dumpWithTimeout(pid, remainingTime);















                    remainingTime -= timeTaken;















                    if (remainingTime <= 0) {













                            Slog.e(TAG, "Aborting stack trace dump (current extra pid=" + stats.pid +













                        Slog.e(TAG, "Aborting stack trace dump (current extra pid=" + pid +















                                "); deadline exceeded.");















                        return;















                    }





























                    if (DEBUG_ANR) {













                            Slog.d(TAG, "Done with extra pid " + stats.pid + " in " + timeTaken + "ms");













                        }













                    } else if (DEBUG_ANR) {













                        Slog.d(TAG, "Skipping next CPU consuming process, not a java proc: "













                                + stats.pid);













                        Slog.d(TAG, "Done with extra pid " + pid + " in " + timeTaken + "ms");















                    }















                }















            }










@@ -5606,7 +5611,7 @@ public class ActivityManagerService extends IActivityManager.Stub













            if (app != null) {















                ArrayList<Integer> firstPids = new ArrayList<Integer>();















                firstPids.add(app.pid);













                dumpStackTraces(tracesPath, firstPids, null, null, null);













                dumpStackTraces(tracesPath, firstPids, null, null);















            }





























            File lastTracesFile = null;