Further bug fix of WifiChannelUtilization.

The absolute values of ccaBusyTime and onTime of link layer stats are
sometimes incorrect (for example, ccaBusyTime is much larger than
onTime) although the delta between two reports seem still correct.

To mitigate the issue,
1) avoid using their absolute value as much as possible. If
channelStatsMap cache is empty for current frequency, refresh the
cache even if device is stationary or cache was updated recently.
2) If estimated utilization ratio is very close to 1, assume it is
due to invalid HW report and return BssLoad.INVALID.

Test: manual
Test: atest com.android.server.wifi
Bug: 150801577
Change-Id: I4700d0d7bf1e57ca7d503e2da290a3320bd9f3f7

1 files changed, 29 insertions, 15 deletions

diff --git a/tests/wifitests/src/com/android/server/wifi/WifiChannelUtilizationTest.java b/tests/wifitests/src/com/android/server/wifi/WifiChannelUtilizationTest.java
index c9ba95d41..31fc7b7a9 100644
--- a/tests/wifitests/src/com/android/server/wifi/WifiChannelUtilizationTest.java
+++ b/tests/wifitests/src/com/android/server/wifi/WifiChannelUtilizationTest.java
@@ -99,7 +99,7 @@ public class WifiChannelUtilizationTest extends WifiBaseTest {
         ChannelStats cs = new ChannelStats();
         cs.frequency = freq;
         cs.radioOnTimeMs = RADIO_ON_TIME_DIFF_MIN_MS * 2;
-        cs.ccaBusyTimeMs = RADIO_ON_TIME_DIFF_MIN_MS * 20;
+        cs.ccaBusyTimeMs = RADIO_ON_TIME_DIFF_MIN_MS * 2 * 19 / 20;
         llstats.channelStatsMap.put(freq, cs);
         mWifiChannelUtilization.refreshChannelStatsAndChannelUtilization(llstats, UNKNOWN_FREQ);
         assertEquals(INVALID, mWifiChannelUtilization.getUtilizationRatio(freq));
@@ -133,7 +133,7 @@ public class WifiChannelUtilizationTest extends WifiBaseTest {
     }
 
     @Test
-    public void verifyTwoReadChanStatsRefWithLast() throws Exception {
+    public void verifyTwoReadChanStatsWithLargeTimeGap() throws Exception {
         WifiLinkLayerStats llstats1 = new WifiLinkLayerStats();
         int freq = 5180;
         ChannelStats cs1 = new ChannelStats();
@@ -161,7 +161,7 @@ public class WifiChannelUtilizationTest extends WifiBaseTest {
     }
 
     @Test
-    public void verifyTwoReadChanStatsRefWithZero() throws Exception {
+    public void verifyTwoReadChanStatsWithSmallTimeGap() throws Exception {
         WifiLinkLayerStats llstats1 = new WifiLinkLayerStats();
         int freq = 5180;
         ChannelStats cs1 = new ChannelStats();
@@ -183,7 +183,8 @@ public class WifiChannelUtilizationTest extends WifiBaseTest {
         when(mClock.getElapsedSinceBootMillis()).thenReturn(currentTimeStamp);
         mWifiChannelUtilization.refreshChannelStatsAndChannelUtilization(llstats2, UNKNOWN_FREQ);
 
-        assertEquals(cs2.ccaBusyTimeMs * MAX_CHANNEL_UTILIZATION / cs2.radioOnTimeMs,
+        assertEquals((cs2.ccaBusyTimeMs - cs1.ccaBusyTimeMs) * MAX_CHANNEL_UTILIZATION
+                / (cs2.radioOnTimeMs - cs1.radioOnTimeMs),
                 mWifiChannelUtilization.getUtilizationRatio(freq));
     }
 
@@ -231,7 +232,7 @@ public class WifiChannelUtilizationTest extends WifiBaseTest {
     }
 
     @Test
-    public void verifyThreeReadChanStatsRefWithLast() throws Exception {
+    public void verifyThreeReadChanStatsLargeTimeGap() throws Exception {
         WifiLinkLayerStats llstats1 = new WifiLinkLayerStats();
         int freq = 5180;
         ChannelStats cs1 = new ChannelStats();
@@ -269,7 +270,7 @@ public class WifiChannelUtilizationTest extends WifiBaseTest {
     }
 
     @Test
-    public void verifyThreeReadChanStatsFirstTwoReadAreTooRecent() throws Exception {
+    public void verifyThreeReadChanStatsSmallTimeGap() throws Exception {
         WifiLinkLayerStats llstats1 = new WifiLinkLayerStats();
         int freq = 5180;
         ChannelStats cs1 = new ChannelStats();
@@ -296,7 +297,8 @@ public class WifiChannelUtilizationTest extends WifiBaseTest {
         when(mClock.getElapsedSinceBootMillis()).thenReturn(currentTimeStamp);
         mWifiChannelUtilization.refreshChannelStatsAndChannelUtilization(llstats3, UNKNOWN_FREQ);
 
-        assertEquals(cs3.ccaBusyTimeMs * MAX_CHANNEL_UTILIZATION / cs3.radioOnTimeMs,
+        assertEquals((cs3.ccaBusyTimeMs - cs1.ccaBusyTimeMs) * MAX_CHANNEL_UTILIZATION
+                / (cs3.radioOnTimeMs - cs1.radioOnTimeMs),
                 mWifiChannelUtilization.getUtilizationRatio(freq));
     }
 
@@ -348,13 +350,22 @@ public class WifiChannelUtilizationTest extends WifiBaseTest {
         WifiLinkLayerStats llstats1 = new WifiLinkLayerStats();
         int freq = 5180;
         ChannelStats cs1 = new ChannelStats();
-        cs1.frequency = freq;
-        cs1.radioOnTimeMs = RADIO_ON_TIME_DIFF_MIN_MS / 4;
-        cs1.ccaBusyTimeMs = 20;
+        cs1.radioOnTimeMs = RADIO_ON_TIME_DIFF_MIN_MS / 8;
+        cs1.ccaBusyTimeMs = 10;
         llstats1.channelStatsMap.put(freq, cs1);
+        long currentTimeStamp = 0;
+        when(mClock.getElapsedSinceBootMillis()).thenReturn(currentTimeStamp);
+        mWifiChannelUtilization.refreshChannelStatsAndChannelUtilization(llstats1, freq);
 
-        mWifiChannelUtilization.refreshChannelStatsAndChannelUtilization(llstats1, UNKNOWN_FREQ);
-        mWifiChannelUtilization.refreshChannelStatsAndChannelUtilization(llstats1, UNKNOWN_FREQ);
+        WifiLinkLayerStats llstats2 = new WifiLinkLayerStats();
+        ChannelStats cs2 = new ChannelStats();
+        cs2.frequency = freq;
+        cs2.radioOnTimeMs = RADIO_ON_TIME_DIFF_MIN_MS / 4;
+        cs2.ccaBusyTimeMs = 20;
+        llstats2.channelStatsMap.put(freq, cs2);
+        currentTimeStamp = 1 + DEFAULT_CACHE_UPDATE_INTERVAL_MIN_MS;
+        when(mClock.getElapsedSinceBootMillis()).thenReturn(currentTimeStamp);
+        mWifiChannelUtilization.refreshChannelStatsAndChannelUtilization(llstats2, freq);
 
         WifiLinkLayerStats llstats3 = new WifiLinkLayerStats();
         ChannelStats cs3 = new ChannelStats();
@@ -362,11 +373,12 @@ public class WifiChannelUtilizationTest extends WifiBaseTest {
         cs3.radioOnTimeMs = RADIO_ON_TIME_DIFF_MIN_MS * 2;
         cs3.ccaBusyTimeMs = 70;
         llstats3.channelStatsMap.put(freq, cs3);
-        long currentTimeStamp = DEFAULT_CACHE_UPDATE_INTERVAL_MIN_MS;
+        currentTimeStamp = 5 + DEFAULT_CACHE_UPDATE_INTERVAL_MIN_MS;
         when(mClock.getElapsedSinceBootMillis()).thenReturn(currentTimeStamp);
-        mWifiChannelUtilization.refreshChannelStatsAndChannelUtilization(llstats3, UNKNOWN_FREQ);
+        mWifiChannelUtilization.refreshChannelStatsAndChannelUtilization(llstats3, freq);
 
-        assertEquals(cs3.ccaBusyTimeMs * MAX_CHANNEL_UTILIZATION / cs3.radioOnTimeMs,
+        assertEquals((cs3.ccaBusyTimeMs - cs1.ccaBusyTimeMs) * MAX_CHANNEL_UTILIZATION
+                / (cs3.radioOnTimeMs - cs1.radioOnTimeMs),
                 mWifiChannelUtilization.getUtilizationRatio(freq));
     }
 
@@ -375,6 +387,8 @@ public class WifiChannelUtilizationTest extends WifiBaseTest {
         WifiLinkLayerStats llstats1 = new WifiLinkLayerStats();
         int freq = 5180;
         ChannelStats cs1 = new ChannelStats();
+        cs1.radioOnTimeMs = RADIO_ON_TIME_DIFF_MIN_MS / 8;
+        cs1.ccaBusyTimeMs = 10;
         llstats1.channelStatsMap.put(freq, cs1);
         long currentTimeStamp = 0;
         when(mClock.getElapsedSinceBootMillis()).thenReturn(currentTimeStamp);