sched_policy.c revision 805d67ab11c1bb21d494459d6167f5f67f0002eb 
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 0
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        LOGE("add_tid_to_cgroup failed to open '%s' (%s)\n", path, strerror(errno));
57        return -1;
58    }
59
60    sprintf(text, "%d", tid);
61    if (write(fd, text, strlen(text)) < 0) {
62        close(fd);
63        return -1;
64    }
65
66    close(fd);
67    return 0;
68}
69
70static inline void initialize()
71{
72    if (__sys_supports_schedgroups < 0) {
73        if (!access("/dev/cpuctl/tasks", F_OK)) {
74            __sys_supports_schedgroups = 1;
75        } else {
76            __sys_supports_schedgroups = 0;
77        }
78    }
79}
80
81/*
82 * Try to get the scheduler group.
83 *
84 * The data from /proc/<pid>/cgroup looks like:
85 *  2:cpu:/bg_non_interactive
86 *
87 * We return the part after the "/", which will be an empty string for
88 * the default cgroup.  If the string is longer than "bufLen", the string
89 * will be truncated.
90 */
91static int getSchedulerGroup(int tid, char* buf, size_t bufLen)
92{
93#ifdef HAVE_ANDROID_OS
94    char pathBuf[32];
95    char readBuf[256];
96    ssize_t count;
97    int fd;
98
99    snprintf(pathBuf, sizeof(pathBuf), "/proc/%d/cgroup", tid);
100    if ((fd = open(pathBuf, O_RDONLY)) < 0) {
101        return -1;
102    }
103
104    count = read(fd, readBuf, sizeof(readBuf));
105    if (count <= 0) {
106        close(fd);
107        errno = ENODATA;
108        return -1;
109    }
110    close(fd);
111
112    readBuf[--count] = '\0';    /* remove the '\n', now count==strlen */
113
114    char* cp = strchr(readBuf, '/');
115    if (cp == NULL) {
116        readBuf[sizeof(readBuf)-1] = '\0';
117        errno = ENODATA;
118        return -1;
119    }
120
121    memcpy(buf, cp+1, count);   /* count-1 for cp+1, count+1 for NUL */
122    return 0;
123#else
124    errno = ENOSYS;
125    return -1;
126#endif
127}
128
129int get_sched_policy(int tid, SchedPolicy *policy)
130{
131    initialize();
132
133    if (__sys_supports_schedgroups) {
134        char grpBuf[32];
135        if (getSchedulerGroup(tid, grpBuf, sizeof(grpBuf)) < 0)
136            return -1;
137        if (grpBuf[0] == '\0') {
138            *policy = SP_FOREGROUND;
139        } else if (!strcmp(grpBuf, "bg_non_interactive")) {
140            *policy = SP_BACKGROUND;
141        } else {
142            errno = ERANGE;
143            return -1;
144        }
145    } else {
146        int rc = sched_getscheduler(tid);
147        if (rc < 0)
148            return -1;
149        else if (rc == SCHED_NORMAL)
150            *policy = SP_FOREGROUND;
151        else if (rc == SCHED_BATCH)
152            *policy = SP_BACKGROUND;
153        else {
154            errno = ERANGE;
155            return -1;
156        }
157    }
158    return 0;
159}
160
161int set_sched_policy(int tid, SchedPolicy policy)
162{
163    initialize();
164
165#if POLICY_DEBUG
166    char statfile[64];
167    char statline[1024];
168    char thread_name[255];
169    int fd;
170
171    sprintf(statfile, "/proc/%d/stat", tid);
172    memset(thread_name, 0, sizeof(thread_name));
173
174    fd = open(statfile, O_RDONLY);
175    if (fd >= 0) {
176        int rc = read(fd, statline, 1023);
177        close(fd);
178        statline[rc] = 0;
179        char *p = statline;
180        char *q;
181
182        for (p = statline; *p != '('; p++);
183        p++;
184        for (q = p; *q != ')'; q++);
185
186        strncpy(thread_name, p, (q-p));
187    }
188    if (policy == SP_BACKGROUND) {
189        LOGD("vvv tid %d (%s)", tid, thread_name);
190    } else if (policy == SP_FOREGROUND) {
191        LOGD("^^^ tid %d (%s)", tid, thread_name);
192    } else {
193        LOGD("??? tid %d (%s)", tid, thread_name);
194    }
195#endif
196
197    if (__sys_supports_schedgroups) {
198        const char *grp = "";
199
200        if (policy == SP_BACKGROUND) {
201            grp = "bg_non_interactive";
202        }
203
204        if (add_tid_to_cgroup(tid, grp)) {
205            if (errno != ESRCH && errno != ENOENT)
206                return -errno;
207        }
208    } else {
209        struct sched_param param;
210
211        param.sched_priority = 0;
212        sched_setscheduler(tid,
213                           (policy == SP_BACKGROUND) ?
214                            SCHED_BATCH : SCHED_NORMAL,
215                           &param);
216    }
217
218    return 0;
219}
220
221#endif /* HAVE_SCHED_H */
222