sched_policy.c revision c0dfca7ae1f6016461235552091c2cacacca82a2 
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#ifdef HAVE_SCHED_H
27
28#include <sched.h>
29
30#include <cutils/sched_policy.h>
31
32#ifndef SCHED_NORMAL
33  #define SCHED_NORMAL 0
34#endif
35
36#ifndef SCHED_BATCH
37  #define SCHED_BATCH 3
38#endif
39
40static int __sys_supports_schedgroups = -1;
41
42static int add_tid_to_cgroup(int tid, const char *grp_name)
43{
44    int fd;
45    char path[255];
46    char text[64];
47
48    sprintf(path, "/dev/cpuctl/%s/tasks", grp_name);
49
50    if ((fd = open(path, O_WRONLY)) < 0)
51        return -1;
52
53    sprintf(text, "%d", tid);
54    if (write(fd, text, strlen(text)) < 0) {
55        close(fd);
56        return -1;
57    }
58
59    close(fd);
60    return 0;
61}
62
63static inline void initialize()
64{
65    if (__sys_supports_schedgroups < 0) {
66        if (!access("/dev/cpuctl/tasks", F_OK)) {
67            __sys_supports_schedgroups = 1;
68        } else {
69            __sys_supports_schedgroups = 0;
70        }
71    }
72}
73
74/*
75 * Try to get the scheduler group.
76 *
77 * The data from /proc/<pid>/cgroup looks like:
78 *  2:cpu:/bg_non_interactive
79 *
80 * We return the part after the "/", which will be an empty string for
81 * the default cgroup.  If the string is longer than "bufLen", the string
82 * will be truncated.
83 */
84static int getSchedulerGroup(int tid, char* buf, size_t bufLen)
85{
86#ifdef HAVE_ANDROID_OS
87    char pathBuf[32];
88    char readBuf[256];
89    ssize_t count;
90    int fd;
91
92    snprintf(pathBuf, sizeof(pathBuf), "/proc/%d/cgroup", tid);
93    if ((fd = open(pathBuf, O_RDONLY)) < 0) {
94        return -1;
95    }
96
97    count = read(fd, readBuf, sizeof(readBuf));
98    if (count <= 0) {
99        close(fd);
100        errno = ENODATA;
101        return -1;
102    }
103    close(fd);
104
105    readBuf[--count] = '\0';    /* remove the '\n', now count==strlen */
106
107    char* cp = strchr(readBuf, '/');
108    if (cp == NULL) {
109        readBuf[sizeof(readBuf)-1] = '\0';
110        errno = ENODATA;
111        return -1;
112    }
113
114    memcpy(buf, cp+1, count);   /* count-1 for cp+1, count+1 for NUL */
115    return 0;
116#else
117    errno = ENOSYS;
118    return -1;
119#endif
120}
121
122int get_sched_policy(int tid, SchedPolicy *policy)
123{
124    initialize();
125
126    if (__sys_supports_schedgroups) {
127        char grpBuf[32];
128        if (getSchedulerGroup(tid, grpBuf, sizeof(grpBuf)) < 0)
129            return -1;
130        if (grpBuf[0] == '\0') {
131            *policy = SP_FOREGROUND;
132        } else if (!strcmp(grpBuf, "bg_non_interactive")) {
133            *policy = SP_BACKGROUND;
134        } else {
135            errno = ERANGE;
136            return -1;
137        }
138    } else {
139        int rc = sched_getscheduler(tid);
140        if (rc < 0)
141            return -1;
142        else if (rc == SCHED_NORMAL)
143            *policy = SP_FOREGROUND;
144        else if (rc == SCHED_BATCH)
145            *policy = SP_BACKGROUND;
146        else {
147            errno = ERANGE;
148            return -1;
149        }
150    }
151    return 0;
152}
153
154int set_sched_policy(int tid, SchedPolicy policy)
155{
156    initialize();
157
158    if (__sys_supports_schedgroups) {
159        const char *grp = NULL;
160
161        if (policy == SP_BACKGROUND) {
162            grp = "bg_non_interactive";
163        }
164
165        if (add_tid_to_cgroup(tid, grp)) {
166            if (errno != ESRCH && errno != ENOENT)
167                return -errno;
168        }
169    } else {
170        struct sched_param param;
171
172        param.sched_priority = 0;
173        sched_setscheduler(tid,
174                           (policy == SP_BACKGROUND) ?
175                            SCHED_BATCH : SCHED_NORMAL,
176                           &param);
177    }
178
179    return 0;
180}
181
182#endif /* HAVE_SCHED_H */
183