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platform_system_core/libcutils/sched_policy.c

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/*
** 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.
*/
#define LOG_TAG "SchedPolicy"
#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <cutils/sched_policy.h>
#include <log/log.h>
#define UNUSED __attribute__((__unused__))
/* Re-map SP_DEFAULT to the system default policy, and leave other values unchanged.
* Call this any place a SchedPolicy is used as an input parameter.
* Returns the possibly re-mapped policy.
*/
static inline SchedPolicy _policy(SchedPolicy p)
{
return p == SP_DEFAULT ? SP_SYSTEM_DEFAULT : p;
}
#if defined(HAVE_ANDROID_OS)
#include <pthread.h>
#include <sched.h>
#include <sys/prctl.h>
#define POLICY_DEBUG 0
// This prctl is only available in Android kernels.
#define PR_SET_TIMERSLACK_PID 41
// timer slack value in nS enforced when the thread moves to background
#define TIMER_SLACK_BG 40000000
#define TIMER_SLACK_FG 50000
static pthread_once_t the_once = PTHREAD_ONCE_INIT;
static int __sys_supports_schedgroups = -1;
// File descriptors open to /dev/cpuctl/../tasks, setup by initialize, or -1 on error.
static int bg_cgroup_fd = -1;
static int fg_cgroup_fd = -1;
// File descriptors open to /dev/cpuset/../tasks, setup by initialize, or -1 on error
static int bg_cpuset_fd = -1;
static int fg_cpuset_fd = -1;
/* Add tid to the scheduling group defined by the policy */
static int add_tid_to_cgroup(int tid, int fd)
{
if (fd < 0) {
SLOGE("add_tid_to_cgroup failed; fd=%d\n", fd);
errno = EINVAL;
return -1;
}
// specialized itoa -- works for tid > 0
char text[22];
char *end = text + sizeof(text) - 1;
char *ptr = end;
*ptr = '\0';
while (tid > 0) {
*--ptr = '0' + (tid % 10);
tid = tid / 10;
}
if (write(fd, ptr, end - ptr) < 0) {
/*
* If the thread is in the process of exiting,
* don't flag an error
*/
if (errno == ESRCH)
return 0;
SLOGW("add_tid_to_cgroup failed to write '%s' (%s); fd=%d\n",
ptr, strerror(errno), fd);
errno = EINVAL;
return -1;
}
return 0;
}
static void __initialize(void) {
char* filename;
if (!access("/dev/cpuctl/tasks", F_OK)) {
__sys_supports_schedgroups = 1;
filename = "/dev/cpuctl/tasks";
fg_cgroup_fd = open(filename, O_WRONLY | O_CLOEXEC);
if (fg_cgroup_fd < 0) {
SLOGE("open of %s failed: %s\n", filename, strerror(errno));
}
filename = "/dev/cpuctl/bg_non_interactive/tasks";
bg_cgroup_fd = open(filename, O_WRONLY | O_CLOEXEC);
if (bg_cgroup_fd < 0) {
SLOGE("open of %s failed: %s\n", filename, strerror(errno));
}
} else {
__sys_supports_schedgroups = 0;
}
#ifdef USE_CPUSETS
if (!access("/dev/cpuset/tasks", F_OK)) {
filename = "/dev/cpuset/foreground/tasks";
fg_cpuset_fd = open(filename, O_WRONLY | O_CLOEXEC);
filename = "/dev/cpuset/background/tasks";
bg_cpuset_fd = open(filename, O_WRONLY | O_CLOEXEC);
}
#endif
}
/*
* Try to get the scheduler group.
*
* The data from /proc/<pid>/cgroup looks (something) like:
* 2:cpu:/bg_non_interactive
* 1:cpuacct:/
*
* We return the part after the "/", which will be an empty string for
* the default cgroup. If the string is longer than "bufLen", the string
* will be truncated.
*/
static int getSchedulerGroup(int tid, char* buf, size_t bufLen)
{
#ifdef HAVE_ANDROID_OS
char pathBuf[32];
char lineBuf[256];
FILE *fp;
snprintf(pathBuf, sizeof(pathBuf), "/proc/%d/cgroup", tid);
if (!(fp = fopen(pathBuf, "r"))) {
return -1;
}
while(fgets(lineBuf, sizeof(lineBuf) -1, fp)) {
char *next = lineBuf;
char *subsys;
char *grp;
size_t len;
/* Junk the first field */
if (!strsep(&next, ":")) {
goto out_bad_data;
}
if (!(subsys = strsep(&next, ":"))) {
goto out_bad_data;
}
if (strcmp(subsys, "cpu")) {
/* Not the subsys we're looking for */
continue;
}
if (!(grp = strsep(&next, ":"))) {
goto out_bad_data;
}
grp++; /* Drop the leading '/' */
len = strlen(grp);
grp[len-1] = '\0'; /* Drop the trailing '\n' */
if (bufLen <= len) {
len = bufLen - 1;
}
strncpy(buf, grp, len);
buf[len] = '\0';
fclose(fp);
return 0;
}
SLOGE("Failed to find cpu subsys");
fclose(fp);
return -1;
out_bad_data:
SLOGE("Bad cgroup data {%s}", lineBuf);
fclose(fp);
return -1;
#else
errno = ENOSYS;
return -1;
#endif
}
int get_sched_policy(int tid, SchedPolicy *policy)
{
if (tid == 0) {
tid = gettid();
}
pthread_once(&the_once, __initialize);
if (__sys_supports_schedgroups) {
char grpBuf[32];
if (getSchedulerGroup(tid, grpBuf, sizeof(grpBuf)) < 0)
return -1;
if (grpBuf[0] == '\0') {
*policy = SP_FOREGROUND;
} else if (!strcmp(grpBuf, "bg_non_interactive")) {
*policy = SP_BACKGROUND;
} else {
errno = ERANGE;
return -1;
}
} else {
int rc = sched_getscheduler(tid);
if (rc < 0)
return -1;
else if (rc == SCHED_NORMAL)
*policy = SP_FOREGROUND;
else if (rc == SCHED_BATCH)
*policy = SP_BACKGROUND;
else {
errno = ERANGE;
return -1;
}
}
return 0;
}
int set_cpuset_policy(int tid, SchedPolicy policy)
{
// in the absence of cpusets, use the old sched policy
#ifndef USE_CPUSETS
return set_sched_policy(tid, policy);
#else
if (tid == 0) {
tid = gettid();
}
policy = _policy(policy);
pthread_once(&the_once, __initialize);
int fd;
switch (policy) {
case SP_BACKGROUND:
fd = bg_cpuset_fd;
break;
case SP_FOREGROUND:
case SP_AUDIO_APP:
case SP_AUDIO_SYS:
fd = fg_cpuset_fd;
break;
default:
fd = -1;
break;
}
if (add_tid_to_cgroup(tid, fd) != 0) {
if (errno != ESRCH && errno != ENOENT)
return -errno;
}
return 0;
#endif
}
int set_sched_policy(int tid, SchedPolicy policy)
{
if (tid == 0) {
tid = gettid();
}
policy = _policy(policy);
pthread_once(&the_once, __initialize);
#if POLICY_DEBUG
char statfile[64];
char statline[1024];
char thread_name[255];
int fd;
sprintf(statfile, "/proc/%d/stat", tid);
memset(thread_name, 0, sizeof(thread_name));
fd = open(statfile, O_RDONLY);
if (fd >= 0) {
int rc = read(fd, statline, 1023);
close(fd);
statline[rc] = 0;
char *p = statline;
char *q;
for (p = statline; *p != '('; p++);
p++;
for (q = p; *q != ')'; q++);
strncpy(thread_name, p, (q-p));
}
switch (policy) {
case SP_BACKGROUND:
SLOGD("vvv tid %d (%s)", tid, thread_name);
break;
case SP_FOREGROUND:
case SP_AUDIO_APP:
case SP_AUDIO_SYS:
SLOGD("^^^ tid %d (%s)", tid, thread_name);
break;
case SP_SYSTEM:
SLOGD("/// tid %d (%s)", tid, thread_name);
break;
default:
SLOGD("??? tid %d (%s)", tid, thread_name);
break;
}
#endif
if (__sys_supports_schedgroups) {
int fd;
switch (policy) {
case SP_BACKGROUND:
fd = bg_cgroup_fd;
break;
case SP_FOREGROUND:
case SP_AUDIO_APP:
case SP_AUDIO_SYS:
fd = fg_cgroup_fd;
break;
default:
fd = -1;
break;
}
if (add_tid_to_cgroup(tid, fd) != 0) {
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);
}
prctl(PR_SET_TIMERSLACK_PID,
policy == SP_BACKGROUND ? TIMER_SLACK_BG : TIMER_SLACK_FG, tid);
return 0;
}
#else
/* Stubs for non-Android targets. */
int set_sched_policy(int tid UNUSED, SchedPolicy policy UNUSED)
{
return 0;
}
int get_sched_policy(int tid UNUSED, SchedPolicy *policy)
{
*policy = SP_SYSTEM_DEFAULT;
return 0;
}
#endif
const char *get_sched_policy_name(SchedPolicy policy)
{
policy = _policy(policy);
static const char * const strings[SP_CNT] = {
[SP_BACKGROUND] = "bg",
[SP_FOREGROUND] = "fg",
[SP_SYSTEM] = " ",
[SP_AUDIO_APP] = "aa",
[SP_AUDIO_SYS] = "as",
};
if ((policy < SP_CNT) && (strings[policy] != NULL))
return strings[policy];
else
return "error";
}
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