Don't assume kernel tick is 100Hz

Bug: 26729731
Change-Id: I094d5fd0e611349becb91d4460bc2e4af255d125

2 files changed, 12 insertions, 5 deletions

diff --git a/core/java/com/android/internal/os/KernelCpuSpeedReader.java b/core/java/com/android/internal/os/KernelCpuSpeedReader.java
index 5b776acf0cc8..3f6ebb9cccff 100644
--- a/core/java/com/android/internal/os/KernelCpuSpeedReader.java
+++ b/core/java/com/android/internal/os/KernelCpuSpeedReader.java
@@ -16,8 +16,11 @@
 package com.android.internal.os;
 
 import android.text.TextUtils;
+import android.system.OsConstants;
 import android.util.Slog;
 
+import libcore.io.Libcore;
+
 import java.io.BufferedReader;
 import java.io.FileReader;
 import java.io.IOException;
@@ -29,7 +32,7 @@ import java.util.Arrays;
  *
  * freq time
  *
- * where time is measured in 1/100 seconds.
+ * where time is measured in jiffies.
  */
 public class KernelCpuSpeedReader {
     private static final String TAG = "KernelCpuSpeedReader";
@@ -38,6 +41,9 @@ public class KernelCpuSpeedReader {
     private final long[] mLastSpeedTimes;
     private final long[] mDeltaSpeedTimes;
 
+    // How long a CPU jiffy is in milliseconds.
+    private final long mJiffyMillis;
+
     /**
      * @param cpuNumber The cpu (cpu0, cpu1, etc) whose state to read.
      */
@@ -46,6 +52,8 @@ public class KernelCpuSpeedReader {
                 cpuNumber);
         mLastSpeedTimes = new long[numSpeedSteps];
         mDeltaSpeedTimes = new long[numSpeedSteps];
+        long jiffyHz = Libcore.os.sysconf(OsConstants._SC_CLK_TCK);
+        mJiffyMillis = 1000/jiffyHz;
     }
 
     /**
@@ -62,8 +70,7 @@ public class KernelCpuSpeedReader {
                 splitter.setString(line);
                 Long.parseLong(splitter.next());
 
-                // The proc file reports time in 1/100 sec, so convert to milliseconds.
-                long time = Long.parseLong(splitter.next()) * 10;
+                long time = Long.parseLong(splitter.next()) * mJiffyMillis;
                 if (time < mLastSpeedTimes[speedIndex]) {
                     // The stats reset when the cpu hotplugged. That means that the time
                     // we read is offset from 0, so the time is the delta.
diff --git a/core/java/com/android/internal/os/ProcessCpuTracker.java b/core/java/com/android/internal/os/ProcessCpuTracker.java
index bf97f1f3e2ed..d8319022f431 100644
--- a/core/java/com/android/internal/os/ProcessCpuTracker.java
+++ b/core/java/com/android/internal/os/ProcessCpuTracker.java
@@ -67,10 +67,10 @@ public class ProcessCpuTracker {
     static final int PROCESS_STAT_UTIME = 2;
     static final int PROCESS_STAT_STIME = 3;
 
-    /** Stores user time and system time in 100ths of a second. */
+    /** Stores user time and system time in jiffies. */
     private final long[] mProcessStatsData = new long[4];
 
-    /** Stores user time and system time in 100ths of a second.  Used for
+    /** Stores user time and system time in jiffies.  Used for
      * public API to retrieve CPU use for a process.  Must lock while in use. */
     private final long[] mSinglePidStatsData = new long[4];