sched_policy.c revision d2e4e46ce4bc29c3328fccfbbbe0590eaa8713f7 
1
2/* libs/cutils/sched_policy.c
3**
4** Copyright 2007, The Android Open Source Project
5**
6** Licensed under the Apache License, Version 2.0 (the "License");
7** you may not use this file except in compliance with the License.
8** You may obtain a copy of the License at
9**
10**     http://www.apache.org/licenses/LICENSE-2.0
11**
12** Unless required by applicable law or agreed to in writing, software
13** distributed under the License is distributed on an "AS IS" BASIS,
14** WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
15** See the License for the specific language governing permissions and
16** limitations under the License.
17*/
18
19#include <stdio.h>
20#include <stdlib.h>
21#include <unistd.h>
22#include <string.h>
23#include <errno.h>
24#include <fcntl.h>
25
26#define LOG_TAG "SchedPolicy"
27#include "cutils/log.h"
28
29#ifdef HAVE_SCHED_H
30
31#include <sched.h>
32
33#include <cutils/sched_policy.h>
34
35#ifndef SCHED_NORMAL
36  #define SCHED_NORMAL 0
37#endif
38
39#ifndef SCHED_BATCH
40  #define SCHED_BATCH 3
41#endif
42
43#define POLICY_DEBUG 1
44
45static int __sys_supports_schedgroups = -1;
46
47static int add_tid_to_cgroup(int tid, const char *grp_name)
48{
49    int fd;
50    char path[255];
51    char text[64];
52
53    sprintf(path, "/dev/cpuctl/%s/tasks", grp_name);
54
55    if ((fd = open(path, O_WRONLY)) < 0)
56        return -1;
57
58    sprintf(text, "%d", tid);
59    if (write(fd, text, strlen(text)) < 0) {
60        close(fd);
61        return -1;
62    }
63
64    close(fd);
65    return 0;
66}
67
68static inline void initialize()
69{
70    if (__sys_supports_schedgroups < 0) {
71        if (!access("/dev/cpuctl/tasks", F_OK)) {
72            __sys_supports_schedgroups = 1;
73        } else {
74            __sys_supports_schedgroups = 0;
75        }
76    }
77}
78
79/*
80 * Try to get the scheduler group.
81 *
82 * The data from /proc/<pid>/cgroup looks like:
83 *  2:cpu:/bg_non_interactive
84 *
85 * We return the part after the "/", which will be an empty string for
86 * the default cgroup.  If the string is longer than "bufLen", the string
87 * will be truncated.
88 */
89static int getSchedulerGroup(int tid, char* buf, size_t bufLen)
90{
91#ifdef HAVE_ANDROID_OS
92    char pathBuf[32];
93    char readBuf[256];
94    ssize_t count;
95    int fd;
96
97    snprintf(pathBuf, sizeof(pathBuf), "/proc/%d/cgroup", tid);
98    if ((fd = open(pathBuf, O_RDONLY)) < 0) {
99        return -1;
100    }
101
102    count = read(fd, readBuf, sizeof(readBuf));
103    if (count <= 0) {
104        close(fd);
105        errno = ENODATA;
106        return -1;
107    }
108    close(fd);
109
110    readBuf[--count] = '\0';    /* remove the '\n', now count==strlen */
111
112    char* cp = strchr(readBuf, '/');
113    if (cp == NULL) {
114        readBuf[sizeof(readBuf)-1] = '\0';
115        errno = ENODATA;
116        return -1;
117    }
118
119    memcpy(buf, cp+1, count);   /* count-1 for cp+1, count+1 for NUL */
120    return 0;
121#else
122    errno = ENOSYS;
123    return -1;
124#endif
125}
126
127int get_sched_policy(int tid, SchedPolicy *policy)
128{
129    initialize();
130
131    if (__sys_supports_schedgroups) {
132        char grpBuf[32];
133        if (getSchedulerGroup(tid, grpBuf, sizeof(grpBuf)) < 0)
134            return -1;
135        if (grpBuf[0] == '\0') {
136            *policy = SP_FOREGROUND;
137        } else if (!strcmp(grpBuf, "bg_non_interactive")) {
138            *policy = SP_BACKGROUND;
139        } else {
140            errno = ERANGE;
141            return -1;
142        }
143    } else {
144        int rc = sched_getscheduler(tid);
145        if (rc < 0)
146            return -1;
147        else if (rc == SCHED_NORMAL)
148            *policy = SP_FOREGROUND;
149        else if (rc == SCHED_BATCH)
150            *policy = SP_BACKGROUND;
151        else {
152            errno = ERANGE;
153            return -1;
154        }
155    }
156    return 0;
157}
158
159int set_sched_policy(int tid, SchedPolicy policy)
160{
161    initialize();
162
163#if POLICY_DEBUG
164    char statfile[64];
165    char statline[1024];
166    char thread_name[255];
167    int fd;
168
169    sprintf(statfile, "/proc/%d/stat", tid);
170    memset(thread_name, 0, sizeof(thread_name));
171
172    fd = open(statfile, O_RDONLY);
173    if (fd >= 0) {
174        int rc = read(fd, statline, 1023);
175        close(fd);
176        statline[rc] = 0;
177        char *p = statline;
178        char *q;
179
180        for (p = statline; *p != '('; p++);
181        p++;
182        for (q = p; *q != ')'; q++);
183
184        strncpy(thread_name, p, (q-p));
185    }
186    if (policy == SP_BACKGROUND) {
187        LOGD("vvv tid %d (%s)", tid, thread_name);
188    } else if (policy == SP_FOREGROUND) {
189        LOGD("^^^ tid %d (%s)", tid, thread_name);
190    } else {
191        LOGD("??? tid %d (%s)", tid, thread_name);
192    }
193#endif
194
195    if (__sys_supports_schedgroups) {
196        const char *grp = NULL;
197
198        if (policy == SP_BACKGROUND) {
199            grp = "bg_non_interactive";
200        }
201
202        if (add_tid_to_cgroup(tid, grp)) {
203            if (errno != ESRCH && errno != ENOENT)
204                return -errno;
205        }
206    } else {
207        struct sched_param param;
208
209        param.sched_priority = 0;
210        sched_setscheduler(tid,
211                           (policy == SP_BACKGROUND) ?
212                            SCHED_BATCH : SCHED_NORMAL,
213                           &param);
214    }
215
216    return 0;
217}
218
219#endif /* HAVE_SCHED_H */
220