Linux 2.6.23开始使用CFS(complete fair schedule),线程Priority不再有效
#include <glib.h>
#include <stdio.h>
static gpointer thread_func(gpointer data)
{
guint64 result = 0;
guint64 i = 0;
for (i = 0; i < 100000000; i++) {
result += i;
}
g_message("Add finished. The result is: %lld", result);
}
int main(int argc, char *argv[])
{
GThread *handle = NULL;
GTimeVal start_time, end_time;
gdouble stime, etime, time_usage;
g_thread_init(NULL);
g_get_current_time(&start_time);
g_message("Create low priority thread now.");
handle = g_thread_create_full((GThreadFunc)thread_func, NULL, 0, TRUE, TRUE, G_THREAD_PRIORITY_LOW, NULL);
if (handle == NULL) {
g_message("Create thread failed, quit.");
return 1;
}
g_thread_join(handle);
g_get_current_time(&end_time);
stime = start_time.tv_sec + (gdouble)start_time.tv_usec / 1000000;
etime = end_time.tv_sec + (gdouble)end_time.tv_usec / 1000000;
time_usage = (etime - stime) * 1000;
g_message("Time elapsed: %.2f ms", time_usage);
return 0;
}
#include <stdio.h>
static gpointer thread_func(gpointer data)
{
guint64 result = 0;
guint64 i = 0;
for (i = 0; i < 100000000; i++) {
result += i;
}
g_message("Add finished. The result is: %lld", result);
}
int main(int argc, char *argv[])
{
GThread *handle = NULL;
GTimeVal start_time, end_time;
gdouble stime, etime, time_usage;
g_thread_init(NULL);
g_get_current_time(&start_time);
g_message("Create low priority thread now.");
handle = g_thread_create_full((GThreadFunc)thread_func, NULL, 0, TRUE, TRUE, G_THREAD_PRIORITY_LOW, NULL);
if (handle == NULL) {
g_message("Create thread failed, quit.");
return 1;
}
g_thread_join(handle);
g_get_current_time(&end_time);
stime = start_time.tv_sec + (gdouble)start_time.tv_usec / 1000000;
etime = end_time.tv_sec + (gdouble)end_time.tv_usec / 1000000;
time_usage = (etime - stime) * 1000;
g_message("Time elapsed: %.2f ms", time_usage);
return 0;
}
可以将这个代码中的线程优先级改成HIGH或URGENT,然后生成两个可执行程序,运行会发现两个程序运行的时间差不多,将系统CPU占用调高,再测试也是一样。或者写一个脚本,同时运行两个程序,也是一样。
这说明现在在pthread中设定线程的priority已经没有效果了。查阅了资料知道,这是因为现在linux默认的调度策略是CFS,完全公平的调度策略,完全根据每个进程消耗的cpu时间来决定下次由哪个进程被调度。如果要改变这种调度策略,那可以使用linux提供的FIFO或RR(round robin)这种类型的策略,这种类型对应到kernel中,是名为realtime的策略,具体在内核sched.c中可以清楚的看到。