SCHED_FIFO線程被Linux中的SCHED_OTHER線程佔用

Question

我已經編寫了測試程序來測試出SCHED_FIFO。我知道SCHED_FIFO不能被SCHED_OTHER線程搶佔。但我無法解釋同一程序多次運行時獲得的結果。

/* Includes */ 
#include <unistd.h>  /* Symbolic Constants */ 
#include <sys/types.h> /* Primitive System Data Types */ 
#include <errno.h>  /* Errors */ 
#include <stdio.h>  /* Input/Output */ 
#include <stdlib.h>  /* General Utilities */ 
#include <pthread.h> /* POSIX Threads */ 
#include <string.h>  /* String handling */ 
#include <sched.h> 
/* prototype for thread routine */ 
void print_message_function (void *ptr); 
void print_message_function1 (void *ptr); 

/* struct to hold data to be passed to a thread 
this shows how multiple data items can be passed to a thread */ 
typedef struct str_thdata 
{ 
int thread_no; 
int thread_value; 
char message[100]; 
    } thdata; 

int main() 
    { 
pthread_t thread1, thread2; /* thread variables */ 
thdata data1, data2;   /* structs to be passed to threads */ 

/* initialize data to pass to thread 1 */ 
data1.thread_no = 1; 
data1.thread_value = 0; 
strcpy(data1.message, "Hello!"); 

/* initialize data to pass to thread 2 */ 
data2.thread_no = 2; 
data2.thread_value = 10000; 
strcpy(data2.message, "Hi!"); 

/* create threads 1 and 2 */  
pthread_create (&thread1, NULL, (void *) &print_message_function, (void *) &data1); 
pthread_create (&thread2, NULL, (void *) &print_message_function1, (void *) &data2); 

/* Main block now waits for both threads to terminate, before it exits 
    If main block exits, both threads exit, even if the threads have not 
    finished their work */ 
pthread_join(thread1, NULL); 
pthread_join(thread2, NULL); 

/* exit */ 
exit(0); 
} /* main() */ 

/** 
* print_message_function is used as the start routine for the threads used 
* it accepts a void pointer 
**/ 
void print_message_function (void *ptr) 
{ 

thdata *data;    
data = (thdata *) ptr; /* type cast to a pointer to thdata */ 

struct sched_param param; 
//int priority=10; 
/* sched_priority will be the priority of the thread */ 
//param.sched_priority = priority; 
/* only supported policy, others will result in ENOTSUP */ 

int policy = SCHED_OTHER; 
/* scheduling parameters of target thread */ 
pthread_setschedparam(pthread_self(), policy, &param); 
printf("Thread %d says sched policy %d \n", data->thread_no, SCHED_OTHER); 
pthread_getschedparam(pthread_self(),&policy,&param); 

printf("Thread %d says %s %d \n", data->thread_no, data->message,policy); 

int i=0; 
/* do the work */ 
printf("Thread %d says %s %d \n", data->thread_no, data->message,(int)pthread_self()); 
for(i=0;i<100;i++) 

printf("Thread %d says %d \n", data->thread_no,data->thread_value++); 
pthread_exit(0); /* exit */ 
} /* print_message_function (void *ptr) */ 



void print_message_function1 (void *ptr) 
{ 

thdata *data;    
data = (thdata *) ptr; /* type cast to a pointer to thdata */ 

struct sched_param param; 
int priority=10; 
/* sched_priority will be the priority of the thread */ 
param.sched_priority = priority; 
/* only supported policy, others will result in ENOTSUP */

int policy = SCHED_FIFO; 
/* scheduling parameters of target thread */ 
pthread_setschedparam(pthread_self(), policy, &param); 
printf("Thread %d says sched policy %d \n", data->thread_no, SCHED_FIFO); 

pthread_getschedparam(pthread_self(),&policy,&param); 

printf("Thread %d says %s %d \n", data->thread_no, data->message,policy); 

int i=0; 
/* do the work */ 
printf("Thread %d says %s %d \n", data->thread_no, data->message,(int)pthread_self()); 
for(i=0;i<100;i++) 

printf("Thread %d says %d \n", data->thread_no,data->thread_value++); 
pthread_exit(0); /* exit */ 
} /* print_message_function (void *ptr) */ 

我有在多個運行意外的結果，其中我看到SCHED_FIFO由SCHED_OTHER線程搶佔，即作爲每個節目，線程2是在FIFO模式中，當線程1是SCHED_OTHER模式。我多次看到thread2被thread1搶佔的地方。

有人可以幫我找出問題嗎？

Answer 1

你可能有效果sysctl的設置，這些設置都是默認值：

kernel.sched_rt_period_us = 1000000 
kernel.sched_rt_runtime_us = 950000 

這意味着，實時線程被允許生豬每1秒週期的只有95％。

另見：Can't provoke Priority Inversion in C++

Answer 2

而且只要在你的IO線程塊，也許從printf報表，另一個線程可調度。