commit 98d30f627ef96ca6e47c9cbcbdcfb63adbeda424
author Peng Xu <pengxu@google.com> Mon Aug 01 18:12:11 2016 -0700
committer Peng Xu <pengxu@google.com> Fri Aug 05 09:18:01 2016 -0700
tree e3703382cbf454daea09e4873cbb263a8eb91bf3
parent 0a21df783892acc5cff0c39c79b0aa602074af7e

Tune SensorService thread priority, lower sensor event latency

Change SensorService priority to SCHED_FIFO 10 to ensure
sensor events to be delivered to apps in consistent short time even
if system is under load.

Bug: 30105910

Change-Id: I5ddf7061b75cf46b54e16476d20bbc888024aa43

services/sensorservice/SensorService.cpp

diff --git a/services/sensorservice/SensorService.cpp b/services/sensorservice/SensorService.cpp
index 0c4dc26..a24740b 100644
--- a/services/sensorservice/SensorService.cpp
+++ b/services/sensorservice/SensorService.cpp
@@ -47,6 +47,7 @@
 
 #include <inttypes.h>
 #include <math.h>
+#include <sched.h>
 #include <stdint.h>
 #include <sys/socket.h>
 #include <sys/stat.h>
@@ -71,6 +72,7 @@
 
 #define SENSOR_SERVICE_DIR "/data/system/sensor_service"
 #define SENSOR_SERVICE_HMAC_KEY_FILE  SENSOR_SERVICE_DIR "/hmac_key"
+#define SENSOR_SERVICE_SCHED_FIFO_PRIORITY 10
 
 // Permissions.
 static const String16 sDump("android.permission.DUMP");
@@ -117,6 +119,15 @@
     return true;
 }
 
+// Set main thread to SCHED_FIFO to lower sensor event latency when system is under load
+void SensorService::enableSchedFifoMode() {
+    struct sched_param param = {0};
+    param.sched_priority = SENSOR_SERVICE_SCHED_FIFO_PRIORITY;
+    if (sched_setscheduler(getTid(), SCHED_FIFO | SCHED_RESET_ON_FORK, &param) != 0) {
+        ALOGE("Couldn't set SCHED_FIFO for SensorService thread");
+    }
+}
+
 void SensorService::onFirstRef() {
     ALOGD("nuSensorService starting...");
     SensorDevice& dev(SensorDevice::getInstance());
@@ -261,6 +272,9 @@
             mAckReceiver = new SensorEventAckReceiver(this);
             mAckReceiver->run("SensorEventAckReceiver", PRIORITY_URGENT_DISPLAY);
             run("SensorService", PRIORITY_URGENT_DISPLAY);
+
+            // priority can only be changed after run
+            enableSchedFifoMode();
         }
     }
 }

services/sensorservice/SensorService.h

diff --git a/services/sensorservice/SensorService.h b/services/sensorservice/SensorService.h
index 68d4154..1e1ea5a 100644
--- a/services/sensorservice/SensorService.h
+++ b/services/sensorservice/SensorService.h
@@ -215,6 +215,8 @@
     // Either read from storage or create a new one.
     static bool initializeHmacKey();
 
+    // Enable SCHED_FIFO priority for thread
+    void enableSchedFifoMode();
 
     static uint8_t sHmacGlobalKey[128];
     static bool sHmacGlobalKeyIsValid;