libcutils: Add abstracted support for setting scheduler policies

Also changes the background policy to use SCHED_BATCH. IDLEPRIO
can cause 100% starvation.

Signed-off-by: San Mehat <san@google.com>

include/cutils/sched_policy.h

@@ -0,0 +1,35 @@
+/*
+ * Copyright (C) 2007 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef __CUTILS_SCHED_POLICY_H
+#define __CUTILS_SCHED_POLICY_H
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+typedef enum {
+    SP_BACKGROUND = 0,
+    SP_FOREGROUND = 1,
+} SchedPolicy;
+
+extern int set_sched_policy(int tid, SchedPolicy policy);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* __CUTILS_SCHED_POLICY_H */ 

libcutils/Android.mk

@@ -36,7 +36,8 @@ commonSources := \
 	record_stream.c \
 	process_name.c \
 	properties.c \
-	threads.c
+	threads.c \
+	sched_policy.c
 
 commonHostSources := \
         ashmem-host.c

libcutils/sched_policy.c

@@ -0,0 +1,84 @@
+/* libs/cutils/sched_policy.c
+**
+** Copyright 2007, The Android Open Source Project
+**
+** Licensed under the Apache License, Version 2.0 (the "License"); 
+** you may not use this file except in compliance with the License. 
+** You may obtain a copy of the License at 
+**
+**     http://www.apache.org/licenses/LICENSE-2.0 
+**
+** Unless required by applicable law or agreed to in writing, software 
+** distributed under the License is distributed on an "AS IS" BASIS, 
+** WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 
+** See the License for the specific language governing permissions and 
+** limitations under the License.
+*/
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <string.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <sched.h>
+#include <linux/sched.h>
+
+#include <cutils/sched_policy.h>
+
+static int add_tid_to_cgroup(int tid, const char *grp_name)
+{
+    int fd;
+    char path[255];
+    char text[64];
+
+    sprintf(path, "/dev/cpuctl/%s/tasks", grp_name);
+
+    if ((fd = open(path, O_WRONLY)) < 0)
+        return -1;
+
+    sprintf(text, "%d", tid);
+    if (write(fd, text, strlen(text)) < 0) {
+        close(fd);
+        return -1;
+    }
+
+    close(fd);
+    return 0;
+}
+
+int set_sched_policy(int tid, SchedPolicy policy)
+{
+    static int __sys_supports_schedgroups = -1;
+
+    if (__sys_supports_schedgroups < 0) {
+        if (!access("/dev/cpuctl/tasks", F_OK)) {
+            __sys_supports_schedgroups = 1;
+        } else {
+            __sys_supports_schedgroups = 0;
+        }
+    }
+
+    if (__sys_supports_schedgroups) {
+        const char *grp = NULL;
+
+        if (policy == SP_BACKGROUND) {
+            grp = "bg_non_interactive";
+        }
+
+        if (add_tid_to_cgroup(tid, grp)) {
+            if (errno != ESRCH && errno != ENOENT)
+                return -errno;
+        }
+    } else {
+        struct sched_param param;
+
+        param.sched_priority = 0;
+        sched_setscheduler(tid,
+                           (policy == SP_BACKGROUND) ?
+                            SCHED_BATCH : SCHED_NORMAL,
+                           &param);
+    }
+
+    return 0;
+}