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platform_system_core/libcutils/sched_policy.cpp
Elliott Hughes 9f49508f36 Rewrite get_sched_policy_name for safety. 
This way you'll get a build time error if you make the usual mistake of
adding to the enum but not adding an entry to the array.

Also improve the unit tests, and fix get_sched_policy_name's incorrect
behavior on invalid inputs.

Bug: N/A
Test: ran tests
Change-Id: Iefcb1ec9ef66267837da7a576c8be3d0cfb16cd0
2018-04-25 14:55:48 -07:00

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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.
*/
#include <cutils/sched_policy.h>
#define LOG_TAG "SchedPolicy"
#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <android-base/macros.h>
#include <log/log.h>
/* 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(__ANDROID__)
#include <pthread.h>
#include <sched.h>
#include <sys/prctl.h>
#define POLICY_DEBUG 0
// 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_timerslack = -1;
// File descriptors open to /dev/cpuset/../tasks, setup by initialize, or -1 on error
static int system_bg_cpuset_fd = -1;
static int bg_cpuset_fd = -1;
static int fg_cpuset_fd = -1;
static int ta_cpuset_fd = -1; // special cpuset for top app
static int rs_cpuset_fd = -1; // special cpuset for screen off restrictions
// File descriptors open to /dev/stune/../tasks, setup by initialize, or -1 on error
static int bg_schedboost_fd = -1;
static int fg_schedboost_fd = -1;
static int ta_schedboost_fd = -1;
static int rt_schedboost_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;
}
/*
If CONFIG_CPUSETS for Linux kernel is set, "tasks" can be found under
/dev/cpuset mounted in init.rc; otherwise, that file does not exist
even though the directory, /dev/cpuset, is still created (by init.rc).
A couple of other candidates (under cpuset mount directory):
notify_on_release
release_agent
Yet another way to decide if cpuset is enabled is to parse
/proc/self/status and search for lines begin with "Mems_allowed".
If CONFIG_PROC_PID_CPUSET is set, the existence "/proc/self/cpuset" can
be used to decide if CONFIG_CPUSETS is set, so we don't have a dependency
on where init.rc mounts cpuset. That's why we'd better require this
configuration be set if CONFIG_CPUSETS is set.
In older releases, this was controlled by build-time configuration.
*/
bool cpusets_enabled() {
static bool enabled = (access("/dev/cpuset/tasks", F_OK) == 0);
return enabled;
}
/*
Similar to CONFIG_CPUSETS above, but with a different configuration
CONFIG_CGROUP_SCHEDTUNE that's in Android common Linux kernel and Linaro
Stable Kernel (LSK), but not in mainline Linux as of v4.9.
In older releases, this was controlled by build-time configuration.
*/
bool schedboost_enabled() {
static bool enabled = (access("/dev/stune/tasks", F_OK) == 0);
return enabled;
}
static void __initialize() {
const char* filename;
if (cpusets_enabled()) {
if (!access("/dev/cpuset/tasks", W_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);
filename = "/dev/cpuset/system-background/tasks";
system_bg_cpuset_fd = open(filename, O_WRONLY | O_CLOEXEC);
filename = "/dev/cpuset/top-app/tasks";
ta_cpuset_fd = open(filename, O_WRONLY | O_CLOEXEC);
filename = "/dev/cpuset/restricted/tasks";
rs_cpuset_fd = open(filename, O_WRONLY | O_CLOEXEC);
if (schedboost_enabled()) {
filename = "/dev/stune/top-app/tasks";
ta_schedboost_fd = open(filename, O_WRONLY | O_CLOEXEC);
filename = "/dev/stune/foreground/tasks";
fg_schedboost_fd = open(filename, O_WRONLY | O_CLOEXEC);
filename = "/dev/stune/background/tasks";
bg_schedboost_fd = open(filename, O_WRONLY | O_CLOEXEC);
filename = "/dev/stune/rt/tasks";
rt_schedboost_fd = open(filename, O_WRONLY | O_CLOEXEC);
}
}
}
char buf[64];
snprintf(buf, sizeof(buf), "/proc/%d/timerslack_ns", getpid());
__sys_supports_timerslack = !access(buf, W_OK);
}
/*
* Returns the path under the requested cgroup subsystem (if it exists)
*
* 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 getCGroupSubsys(int tid, const char* subsys, char* buf, size_t bufLen)
{
#if defined(__ANDROID__)
char pathBuf[32];
char lineBuf[256];
FILE *fp;
snprintf(pathBuf, sizeof(pathBuf), "/proc/%d/cgroup", tid);
if (!(fp = fopen(pathBuf, "re"))) {
return -1;
}
while(fgets(lineBuf, sizeof(lineBuf) -1, fp)) {
char *next = lineBuf;
char *found_subsys;
char *grp;
size_t len;
/* Junk the first field */
if (!strsep(&next, ":")) {
goto out_bad_data;
}
if (!(found_subsys = strsep(&next, ":"))) {
goto out_bad_data;
}
if (strcmp(found_subsys, subsys)) {
/* 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 subsys %s", 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);
char grpBuf[32];
grpBuf[0] = '\0';
if (schedboost_enabled()) {
if (getCGroupSubsys(tid, "schedtune", grpBuf, sizeof(grpBuf)) < 0) return -1;
}
if ((grpBuf[0] == '\0') && cpusets_enabled()) {
if (getCGroupSubsys(tid, "cpuset", grpBuf, sizeof(grpBuf)) < 0) return -1;
}
if (grpBuf[0] == '\0') {
*policy = SP_FOREGROUND;
} else if (!strcmp(grpBuf, "foreground")) {
*policy = SP_FOREGROUND;
} else if (!strcmp(grpBuf, "system-background")) {
*policy = SP_SYSTEM;
} else if (!strcmp(grpBuf, "background")) {
*policy = SP_BACKGROUND;
} else if (!strcmp(grpBuf, "top-app")) {
*policy = SP_TOP_APP;
} 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
if (!cpusets_enabled()) {
return set_sched_policy(tid, policy);
}
if (tid == 0) {
tid = gettid();
}
policy = _policy(policy);
pthread_once(&the_once, __initialize);
int fd = -1;
int boost_fd = -1;
switch (policy) {
case SP_BACKGROUND:
fd = bg_cpuset_fd;
boost_fd = bg_schedboost_fd;
break;
case SP_FOREGROUND:
case SP_AUDIO_APP:
case SP_AUDIO_SYS:
fd = fg_cpuset_fd;
boost_fd = fg_schedboost_fd;
break;
case SP_TOP_APP :
fd = ta_cpuset_fd;
boost_fd = ta_schedboost_fd;
break;
case SP_SYSTEM:
fd = system_bg_cpuset_fd;
break;
case SP_RESTRICTED:
fd = rs_cpuset_fd;
break;
default:
boost_fd = fd = -1;
break;
}
if (add_tid_to_cgroup(tid, fd) != 0) {
if (errno != ESRCH && errno != ENOENT)
return -errno;
}
if (schedboost_enabled()) {
if (boost_fd > 0 && add_tid_to_cgroup(tid, boost_fd) != 0) {
if (errno != ESRCH && errno != ENOENT)
return -errno;
}
}
return 0;
}
static void set_timerslack_ns(int tid, unsigned long slack) {
// v4.6+ kernels support the /proc/<tid>/timerslack_ns interface.
// TODO: once we've backported this, log if the open(2) fails.
if (__sys_supports_timerslack) {
char buf[64];
snprintf(buf, sizeof(buf), "/proc/%d/timerslack_ns", tid);
int fd = open(buf, O_WRONLY | O_CLOEXEC);
if (fd != -1) {
int len = snprintf(buf, sizeof(buf), "%lu", slack);
if (write(fd, buf, len) != len) {
SLOGE("set_timerslack_ns write failed: %s\n", strerror(errno));
}
close(fd);
return;
}
}
// TODO: Remove when /proc/<tid>/timerslack_ns interface is backported.
if ((tid == 0) || (tid == gettid())) {
if (prctl(PR_SET_TIMERSLACK, slack) == -1) {
SLOGE("set_timerslack_ns prctl failed: %s\n", strerror(errno));
}
}
}
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];
snprintf(statfile, sizeof(statfile), "/proc/%d/stat", tid);
memset(thread_name, 0, sizeof(thread_name));
int fd = open(statfile, O_RDONLY | O_CLOEXEC);
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:
case SP_TOP_APP:
SLOGD("^^^ tid %d (%s)", tid, thread_name);
break;
case SP_SYSTEM:
SLOGD("/// tid %d (%s)", tid, thread_name);
break;
case SP_RT_APP:
SLOGD("RT tid %d (%s)", tid, thread_name);
break;
default:
SLOGD("??? tid %d (%s)", tid, thread_name);
break;
}
#endif
if (schedboost_enabled()) {
int boost_fd = -1;
switch (policy) {
case SP_BACKGROUND:
boost_fd = bg_schedboost_fd;
break;
case SP_FOREGROUND:
case SP_AUDIO_APP:
case SP_AUDIO_SYS:
boost_fd = fg_schedboost_fd;
break;
case SP_TOP_APP:
boost_fd = ta_schedboost_fd;
break;
case SP_RT_APP:
boost_fd = rt_schedboost_fd;
break;
default:
boost_fd = -1;
break;
}
if (boost_fd > 0 && add_tid_to_cgroup(tid, boost_fd) != 0) {
if (errno != ESRCH && errno != ENOENT)
return -errno;
}
}
set_timerslack_ns(tid, policy == SP_BACKGROUND ? TIMER_SLACK_BG : TIMER_SLACK_FG);
return 0;
}
#else
/* Stubs for non-Android targets. */
int set_sched_policy(int /*tid*/, SchedPolicy /*policy*/) {
return 0;
}
int get_sched_policy(int /*tid*/, SchedPolicy* policy) {
*policy = SP_SYSTEM_DEFAULT;
return 0;
}
#endif
const char* get_sched_policy_name(SchedPolicy policy) {
policy = _policy(policy);
static const char* const kSchedPolicyNames[] = {
[SP_BACKGROUND] = "bg", [SP_FOREGROUND] = "fg", [SP_SYSTEM] = " ",
[SP_AUDIO_APP] = "aa", [SP_AUDIO_SYS] = "as", [SP_TOP_APP] = "ta",
[SP_RT_APP] = "rt", [SP_RESTRICTED] = "rs",
};
static_assert(arraysize(kSchedPolicyNames) == SP_CNT, "missing name");
if (policy < SP_BACKGROUND || policy >= SP_CNT) {
return "error";
}
return kSchedPolicyNames[policy];
}
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