1 files changed, 80 insertions, 12 deletions

diff --git a/libs/utils/SystemClock.cpp b/libs/utils/SystemClock.cpp
index 8b8ac10..ec2d82e 100644
--- a/libs/utils/SystemClock.cpp
+++ b/libs/utils/SystemClock.cpp
@@ -106,7 +106,74 @@ int64_t uptimeMillis()
  */
 int64_t elapsedRealtime()
 {
+	return nanoseconds_to_milliseconds(elapsedRealtimeNano());
+}
+
+#define METHOD_CLOCK_GETTIME    0
+#define METHOD_IOCTL            1
+#define METHOD_SYSTEMTIME       2
+
+static const char *gettime_method_names[] = {
+    "clock_gettime",
+    "ioctl",
+    "systemTime",
+};
+
+static inline void checkTimeStamps(int64_t timestamp,
+                                   int64_t volatile *prevTimestampPtr,
+                                   int volatile *prevMethodPtr,
+                                   int curMethod)
+{
+    /*
+     * Disable the check for SDK since the prebuilt toolchain doesn't contain
+     * gettid, and int64_t is different on the ARM platform
+     * (ie long vs long long).
+     */
+#ifdef ARCH_ARM
+    int64_t prevTimestamp = *prevTimestampPtr;
+    int prevMethod = *prevMethodPtr;
+
+    if (timestamp < prevTimestamp) {
+        ALOGW("time going backwards: prev %lld(%s) vs now %lld(%s), tid=%d",
+              prevTimestamp, gettime_method_names[prevMethod],
+              timestamp, gettime_method_names[curMethod],
+              gettid());
+    }
+    // NOTE - not atomic and may generate spurious warnings if the 64-bit
+    // write is interrupted or not observed as a whole.
+    *prevTimestampPtr = timestamp;
+    *prevMethodPtr = curMethod;
+#endif
+}
+
+/*
+ * native public static long elapsedRealtimeNano();
+ */
+int64_t elapsedRealtimeNano()
+{
 #ifdef HAVE_ANDROID_OS
+    struct timespec ts;
+    int result;
+    int64_t timestamp;
+    static volatile int64_t prevTimestamp;
+    static volatile int prevMethod;
+
+#if 0
+    /*
+     * b/7100774
+     * clock_gettime appears to have clock skews and can sometimes return
+     * backwards values. Disable its use until we find out what's wrong.
+     */
+    result = clock_gettime(CLOCK_BOOTTIME, &ts);
+    if (result == 0) {
+        timestamp = seconds_to_nanoseconds(ts.tv_sec) + ts.tv_nsec;
+        checkTimeStamps(timestamp, &prevTimestamp, &prevMethod,
+                        METHOD_CLOCK_GETTIME);
+        return timestamp;
+    }
+#endif
+
+    // CLOCK_BOOTTIME doesn't exist, fallback to /dev/alarm
     static int s_fd = -1;
 
     if (s_fd == -1) {
@@ -116,23 +183,24 @@ int64_t elapsedRealtime()
         }
     }
 
-    struct timespec ts;
-    int result = ioctl(s_fd,
+    result = ioctl(s_fd,
             ANDROID_ALARM_GET_TIME(ANDROID_ALARM_ELAPSED_REALTIME), &ts);
 
     if (result == 0) {
-        int64_t when = seconds_to_nanoseconds(ts.tv_sec) + ts.tv_nsec;
-        return (int64_t) nanoseconds_to_milliseconds(when);
-    } else {
-        // XXX: there was an error, probably because the driver didn't
-        // exist ... this should return
-        // a real error, like an exception!
-        int64_t when = systemTime(SYSTEM_TIME_MONOTONIC);
-        return (int64_t) nanoseconds_to_milliseconds(when);
+        timestamp = seconds_to_nanoseconds(ts.tv_sec) + ts.tv_nsec;
+        checkTimeStamps(timestamp, &prevTimestamp, &prevMethod, METHOD_IOCTL);
+        return timestamp;
     }
+
+    // XXX: there was an error, probably because the driver didn't
+    // exist ... this should return
+    // a real error, like an exception!
+    timestamp = systemTime(SYSTEM_TIME_MONOTONIC);
+    checkTimeStamps(timestamp, &prevTimestamp, &prevMethod,
+                    METHOD_SYSTEMTIME);
+    return timestamp;
 #else
-    int64_t when = systemTime(SYSTEM_TIME_MONOTONIC);
-    return (int64_t) nanoseconds_to_milliseconds(when);
+    return systemTime(SYSTEM_TIME_MONOTONIC);
 #endif
 }