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>
diff --git a/libcutils/sched_policy.c b/libcutils/sched_policy.c
new file mode 100644
index 0000000..d363644
--- /dev/null
+++ b/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,
+ ¶m);
+ }
+
+ return 0;
+}