Linux I/O Scheduler--CFQ(下)
Linux I/O Scheduler--CFQ(下)
前文介绍了CFQ调度器的一些概念和结构之间的关系,这里再结合实际的代码,来分析CFQ的工作流程。
Linux I/O Scheduler--CFQ(上)
CFQ调度器的定义如下:
static struct elevator_type iosched_cfq = {
.ops = {
.elevator_merge_fn = cfq_merge,
.elevator_merged_fn = cfq_merged_request,
.elevator_merge_req_fn = cfq_merged_requests,
.elevator_allow_merge_fn = cfq_allow_merge,
.elevator_dispatch_fn = cfq_dispatch_requests,
.elevator_add_req_fn = cfq_insert_request,
.elevator_activate_req_fn = cfq_activate_request,
.elevator_deactivate_req_fn = cfq_deactivate_request,
.elevator_queue_empty_fn = cfq_queue_empty,
.elevator_completed_req_fn = cfq_completed_request,
.elevator_former_req_fn = elv_rb_former_request,
.elevator_latter_req_fn = elv_rb_latter_request,
.elevator_set_req_fn = cfq_set_request,
.elevator_put_req_fn = cfq_put_request,
.elevator_may_queue_fn = cfq_may_queue,
.elevator_init_fn = cfq_init_queue,
.elevator_exit_fn = cfq_exit_queue,
.trim = cfq_free_io_context,
},
.elevator_attrs = cfq_attrs,
.elevator_name = "cfq",
.elevator_owner = THIS_MODULE,
};
可以看到CFQ调度器涉及到的操作函数还是比较多的,这里我只打算选一些和提交bio以及request相关的函数进行分析。在提交bio的时候,如果在通用层寻找可以合并bio的途径失败,要通过cfq_merge()来判断是否能够将bio插入到某个request的bio链表首部
static struct request *
cfq_find_rq_fmerge(struct cfq_data *cfqd, struct bio *bio)
{
struct task_struct *tsk = current;
struct cfq_io_context *cic;
struct cfq_queue *cfqq;
//在进程的io_context中,找到进程特定于块设备的cfq_io_context
cic = cfq_cic_lookup(cfqd, tsk->io_context);
if (!cic)
return NULL;
//根据同步还是异步,确定cfq_queue
cfqq = cic_to_cfqq(cic, cfq_bio_sync(bio));
if (cfqq) {
sector_t sector = bio->bi_sector + bio_sectors(bio);//得到末尾扇区号
//从cfq_queue的红黑树中查找对应的节点
return elv_rb_find(&cfqq->sort_list, sector);
}
return NULL;
}
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