ucore操作系统lab6 —— 调度算法
一、练习零：填写已有实验
二、练习一: 使用 Round Robin 调度算法
首先需要换掉RR调度器的实现，即用default_sched_stride_c覆盖default_sched.c。然后根据此文件和后续文档对Stride度器的相关描述，完成Stride调度算法的实现。
1、比较器定义
7、定义一个c语言类的实现，提供调度算法的切换接口
本实验依赖实验1/2/3/4/5。请把你做的实验2/3/4/5的代码填入本实验中代码中有“LAB1”/“LAB2”/“LAB3”/“LAB4”“LAB5”的注释相应部分。并确保编译通过。注意：为了能够正确执行lab6的测试应用程序，可能需对已完成的实验1/2/3/4/5的代码进行进一步改进。
//LAB6 YOUR CODE : (update LAB5 steps)
/*
* below fields(add in LAB6) in proc_struct need to be initialized
* struct run_queue *rq; // running queue contains Process
* list_entry_t run_link; // the entry linked in run queue
* int time_slice; // time slice for occupying the CPU
* skew_heap_entry_t lab6_run_pool; // FOR LAB6 ONLY: the entry in the run pool
* uint32_t lab6_stride; // FOR LAB6 ONLY: the current stride of the process
* uint32_t lab6_priority; // FOR LAB6 ONLY: the priority of process, set by lab6_set_priority(uint32_t)
*/
proc->state = PROC_UNINIT;
proc->pid = -1;
proc->runs = 0;
proc->kstack = 0;
proc->need_resched = 0;
proc->parent = NULL;
proc->mm = NULL;
memset(&(proc->context), 0, sizeof(struct context));
proc->tf = NULL;
proc->cr3 = boot_cr3;
proc->flags = 0;
memset(proc->name, 0, PROC_NAME_LEN);
proc->wait_state = 0;
proc->cptr = proc->optr = proc->yptr = NULL;
proc->rq = NULL;
proc->run_link.prev = proc->run_link.next = NULL;
proc->time_slice = 0;
proc->lab6_run_pool.left = proc->lab6_run_pool.right = proc->lab6_run_pool.parent = NULL;//斜堆指针初始化
proc->lab6_stride = 0;//步数初始化
proc->lab6_priority = 0;//优先级初始化
}/* LAB6 YOUR CODE */
/* IMPORTANT FUNCTIONS:
* run_timer_list
*----------------------
* you should update your lab5 code (just add ONE or TWO lines of code):
* Every tick, you should update the system time, iterate the timers, and trigger the timers which are end to call scheduler.
* You can use one funcitons to finish all these things.
*/
ticks ++;
assert(current != NULL);
run_timer_list(); //更新定时器，并根据参数调用调度算法
break;二、练习一: 使用 Round Robin 调度算法
理解并分析sched_calss中各个函数指针的用法，并接合Round Robin 调度算法描ucore的调度执行过程
1、执行过程
让所有runnable态的进程分时轮流使用CPU时间。RR调度器维护当前runnable进程的有序运行队列。当前进程的时间片用完之后，调度器将当前进程放置到运行队列的尾部，再从其头部取出进程进行调度。RR调度算法的就绪队列在组织结构上也是一个双向链表，只是增加了一个成员变量，表明在此就绪进程队列中的最大执行时间片。而且在进程控制块proc_struct中增加了一个成员变量time_slice，用来记录进程当前的可运行时间片段。这是由于RR调度算法需要考虑执行进程的运行时间不能太长。在每个timer到时的时候，操作系统会递减当前执行进程的time_slice，当time_slice为0时，就意味着这个进程运行了一段时间（这个时间片段称为进程的时间片），需要把CPU让给其他进程执行，于是操作系统就需要让此进程重新回到rq的队列尾，且重置此进程的时间片为就绪队列的成员变量最大时间片max_time_slice值，然后再从rq的队列头取出一个新的进程执行。下面来分析一下其调度算法的实现。
2、算法实现
RR_init完成了对进程队列的初始化
static void
RR_init(struct run_queue *rq) {
list_init(&(rq->run_list));
rq->proc_num = 0;
}static void
RR_enqueue(struct run_queue *rq, struct proc_struct *proc) {
assert(list_empty(&(proc->run_link)));
list_add_before(&(rq->run_list), &(proc->run_link));
if (proc->time_slice == 0 || proc->time_slice > rq->max_time_slice) {
proc->time_slice = rq->max_time_slice;
}
proc->rq = rq;
rq->proc_num ++;
}static void
RR_dequeue(struct run_queue *rq, struct proc_struct *proc) {
assert(!list_empty(&(proc->run_link)) && proc->rq == rq);
list_del_init(&(proc->run_link));
rq->proc_num --;
}static struct proc_struct *
RR_pick_next(struct run_queue *rq) {
list_entry_t *le = list_next(&(rq->run_list));
if (le != &(rq->run_list)) {
return le2proc(le, run_link);
}
return NULL;
}static void
RR_proc_tick(struct run_queue *rq, struct proc_struct *proc) {
if (proc->time_slice > 0) {
proc->time_slice --;
}
if (proc->time_slice == 0) {
proc->need_resched = 1;
}
}struct sched_class default_sched_class = {
.name = "RR_scheduler",
.init = RR_init,
.enqueue = RR_enqueue,
.dequeue = RR_dequeue,
.pick_next = RR_pick_next,
.proc_tick = RR_proc_tick,
};三、练习二: 实现 Stride Scheduling 调度算法
首先需要换掉RR调度器的实现，即用default_sched_stride_c覆盖default_sched.c。然后根据此文件和后续文档对Stride度器的相关描述，完成Stride调度算法的实现。
1、比较器定义
/* You should define the BigStride constant here*/
/* LAB6: YOUR CODE */
#define BIG_STRIDE 0x7FFFFFFF /* 定义一个大整数处以优先级 */
/* The compare function for two skew_heap_node_t's and the
* corresponding procs*/
static int
proc_stride_comp_f(void *a, void *b)
{
struct proc_struct *p = le2proc(a, lab6_run_pool);
struct proc_struct *q = le2proc(b, lab6_run_pool);
int32_t c = p->lab6_stride - q->lab6_stride;//步数相减，通过正负比较大小关系
if (c > 0) return 1;
else if (c == 0) return 0;
else return -1;
}2、运行队列初始化
/*
* stride_init initializes the run-queue rq with correct assignment for
* member variables, including:
*
* - run_list: should be a empty list after initialization.
* - lab6_run_pool: NULL
* - proc_num: 0
* - max_time_slice: no need here, the variable would be assigned by the caller.
*
* hint: see proj13.1/libs/list.h for routines of the list structures.
*/
static void
stride_init(struct run_queue *rq) {
/* LAB6: YOUR CODE */
list_init(&(rq->run_list));//初始化调度器类的信息
rq->lab6_run_pool = NULL;//初始化当前的运行队列为一个空的容器结构。
rq->proc_num = 0;//设置rq->proc_num为 0
}
/*
* stride_enqueue inserts the process ``proc'' into the run-queue
* ``rq''. The procedure should verify/initialize the relevant members
* of ``proc'', and then put the ``lab6_run_pool'' node into the
* queue(since we use priority queue here). The procedure should also
* update the meta date in ``rq'' structure.
*
* proc->time_slice denotes the time slices allocation for the
* process, which should set to rq->max_time_slice.
*
* hint: see proj13.1/libs/skew_heap.h for routines of the priority
* queue structures.
*/
static void
stride_enqueue(struct run_queue *rq, struct proc_struct *proc) {
/* LAB6: YOUR CODE */
#if USE_SKEW_HEAP
rq->lab6_run_pool = //在使用优先队列的实现中表示当前优先队列的头元素
skew_heap_insert(rq->lab6_run_pool, &(proc->lab6_run_pool), proc_stride_comp_f);//比较队头元素与当前进程的步数大小，选择步数最小的运行
#else
assert(list_empty(&(proc->run_link)));
list_add_before(&(rq->run_list), &(proc->run_link));//将 proc插入放入运行队列中去
#endif
if (proc->time_slice == 0 || proc->time_slice > rq->max_time_slice) {//初始化时间片
proc->time_slice = rq->max_time_slice;
}
proc->rq = rq;
rq->proc_num ++;
}4、出队操作
/*
* stride_dequeue removes the process ``proc'' from the run-queue
* ``rq'', the operation would be finished by the skew_heap_remove
* operations. Remember to update the ``rq'' structure.
*
* hint: see proj13.1/libs/skew_heap.h for routines of the priority
* queue structures.
*/
static void
stride_dequeue(struct run_queue *rq, struct proc_struct *proc) {
/* LAB6: YOUR CODE */
#if USE_SKEW_HEAP
rq->lab6_run_pool =
skew_heap_remove(rq->lab6_run_pool, &(proc->lab6_run_pool), proc_stride_comp_f);// 在斜堆中删除相应元素
#else
assert(!list_empty(&(proc->run_link)) && proc->rq == rq);
list_del_init(&(proc->run_link));// 从运行队列中删除相应元素
#endif
rq->proc_num --;
}/*
* stride_pick_next pick the element from the ``run-queue'', with the
* minimum value of stride, and returns the corresponding process
* pointer. The process pointer would be calculated by macro le2proc,
* see proj13.1/kern/process/proc.h for definition. Return NULL if
* there is no process in the queue.
*
* When one proc structure is selected, remember to update the stride
* property of the proc. (stride += BIG_STRIDE / priority)
*
* hint: see proj13.1/libs/skew_heap.h for routines of the priority
* queue structures.
*/
static struct proc_struct *
stride_pick_next(struct run_queue *rq) {
/* LAB6: YOUR CODE */
#if USE_SKEW_HEAP
if (rq->lab6_run_pool == NULL) return NULL;
struct proc_struct *p = le2proc(rq->lab6_run_pool, lab6_run_pool); //找到相应指针指向rq->lab6_run_pool
#else
list_entry_t *le = list_next(&(rq->run_list));
if (le == &rq->run_list)
return NULL;
struct proc_struct *p = le2proc(le, run_link);
le = list_next(le);
while (le != &rq->run_list)
{
struct proc_struct *q = le2proc(le, run_link);
if ((int32_t)(p->lab6_stride - q->lab6_stride) > 0)
p = q;
le = list_next(le);
}
#endif
if (p->lab6_priority == 0)//优先级设置
p->lab6_stride += BIG_STRIDE;//步长为0则设置为最大步长保持相减的有效性
else p->lab6_stride += BIG_STRIDE / p->lab6_priority;//步长设置为优先级的倒数
return p;
}/*
* stride_proc_tick works with the tick event of current process. You
* should check whether the time slices for current process is
* exhausted and update the proc struct ``proc''. proc->time_slice
* denotes the time slices left for current
* process. proc->need_resched is the flag variable for process
* switching.
*/
static void
stride_proc_tick(struct run_queue *rq, struct proc_struct *proc) {
/* LAB6: YOUR CODE */
if (proc->time_slice > 0) {
proc->time_slice --;
}
if (proc->time_slice == 0) {
proc->need_resched = 1;
}
}7、定义一个c语言类的实现，提供调度算法的切换接口
struct sched_class default_sched_class = {
.name = "stride_scheduler",
.init = stride_init,
.enqueue = stride_enqueue,
.dequeue = stride_dequeue,
.pick_next = stride_pick_next,
.proc_tick = stride_proc_tick,
};实验结果：
