[英]How to use sched_getaffinity and sched_setaffinity in Linux from C?
I am trying to:我在尝试着:
Run 16 copies concurrently with processor pinning (2 copies per core)与处理器固定同时运行 16 个副本(每个内核 2 个副本)
Run 8 copies concurrently with processor pinning (2 copies per core) and flipping processor core to the furthest core after certain function say function 1 finishes.与处理器固定同时运行 8 个副本(每个内核 2 个副本),并在某些功能说功能 1 完成后将处理器内核翻转到最远的内核。
The problem I am facing is how to select the farthest processor.我面临的问题是如何选择最远的处理器。
Some friends suggested to use sched_getaffinity and sched_setaffinity but I count not find any good examples.有些朋友建议使用 sched_getaffinity 和 sched_setaffinity 但我数了数没有找到任何好的例子。
To use sched_setaffinity to make the current process run on core 7 you do this:要使用 sched_setaffinity 使当前进程在核心 7 上运行,您可以执行以下操作:
cpu_set_t my_set; /* Define your cpu_set bit mask. */
CPU_ZERO(&my_set); /* Initialize it all to 0, i.e. no CPUs selected. */
CPU_SET(7, &my_set); /* set the bit that represents core 7. */
sched_setaffinity(0, sizeof(cpu_set_t), &my_set); /* Set affinity of tihs process to */
/* the defined mask, i.e. only 7. */
See http://linux.die.net/man/2/sched_setaffinity & http://www.gnu.org/software/libc/manual/html_node/CPU-Affinity.html for more info.有关更多信息,请参阅http://linux.die.net/man/2/sched_setaffinity & http://www.gnu.org/software/libc/manual/html_node/CPU-Affinity.html 。
Minimal runnable example最小的可运行示例
In this example, we get the affinity, modify it, and check if it has taken effect with sched_getcpu()
.在这个例子中,我们获取了affinity,修改它,然后用
sched_getcpu()
检查它是否生效。
main.c主文件
#define _GNU_SOURCE
#include <assert.h>
#include <sched.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
void print_affinity() {
cpu_set_t mask;
long nproc, i;
if (sched_getaffinity(0, sizeof(cpu_set_t), &mask) == -1) {
perror("sched_getaffinity");
assert(false);
}
nproc = sysconf(_SC_NPROCESSORS_ONLN);
printf("sched_getaffinity = ");
for (i = 0; i < nproc; i++) {
printf("%d ", CPU_ISSET(i, &mask));
}
printf("\n");
}
int main(void) {
cpu_set_t mask;
print_affinity();
printf("sched_getcpu = %d\n", sched_getcpu());
CPU_ZERO(&mask);
CPU_SET(0, &mask);
if (sched_setaffinity(0, sizeof(cpu_set_t), &mask) == -1) {
perror("sched_setaffinity");
assert(false);
}
print_affinity();
/* TODO is it guaranteed to have taken effect already? Always worked on my tests. */
printf("sched_getcpu = %d\n", sched_getcpu());
return EXIT_SUCCESS;
}
Compile and run:编译并运行:
gcc -ggdb3 -O0 -std=c99 -Wall -Wextra -pedantic -o main.out main.c
./main.out
Sample output:示例输出:
sched_getaffinity = 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
sched_getcpu = 9
sched_getaffinity = 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
sched_getcpu = 0
Which means that:意思就是:
It is also fun to run this program through taskset
:通过
taskset
运行这个程序也很有趣:
taskset -c 1,3 ./a.out
Which gives output of form:这给出了以下形式的输出:
sched_getaffinity = 0 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0
sched_getcpu = 2
sched_getaffinity = 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
sched_getcpu = 0
and so we see that it limited the affinity from the start.所以我们看到它从一开始就限制了亲和力。
This works because the affinity is inherited by child processes, which taskset
is forking: How to prevent inheriting CPU affinity by child forked process?这是有效的,因为关联是由子进程继承的,哪个
taskset
正在分叉: 如何防止子进程继承 CPU 关联?
nproc
respects sched_getaffinity
by default as shown at: How to find out the number of CPUs using python默认情况下,
nproc
尊重sched_getaffinity
,如下所示: How to find out the number of CPUs using python
Python: os.sched_getaffinity
and os.sched_setaffinity
Python:
os.sched_getaffinity
和os.sched_setaffinity
See: How to find out the number of CPUs using python请参阅: 如何使用python找出CPU的数量
Tested in Ubuntu 16.04.在 Ubuntu 16.04 中测试。
Don't use CPU_SETSIZE as cpusetsize parameter for sched_[set|get]affinity.不要使用 CPU_SETSIZE 作为 sched_[set|get]affinity 的 cpusetsize 参数。 The names are misleading but this is wrong.
这些名称具有误导性,但这是错误的。 The macro CPU_SETSIZE is (quoting man 3 cpu_set) "a value one greater than the maximum CPU number that can be stored in cpu_set_t."
宏 CPU_SETSIZE 是(引用 man 3 cpu_set)“比可以存储在 cpu_set_t 中的最大 CPU 数量大 1 的值”。 You have to use
你必须使用
sched_setaffinity(0, sizeof(cpu_set_t), &my_set);
instead.反而。
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