diff --git a/study/kernel/01-process/02-create/06-thread_info/images/20140506.jpg b/study/kernel/01-process/02-create/06-thread_info/images/20140506.jpg
new file mode 100644
index 0000000..7f29581
Binary files /dev/null and b/study/kernel/01-process/02-create/06-thread_info/images/20140506.jpg differ
diff --git a/study/kernel/01-process/05-schedule/06-main_scheduler/README.md b/study/kernel/01-process/05-schedule/06-main_scheduler/README.md
index ab0d942..bab9231 100644
--- a/study/kernel/01-process/05-schedule/06-main_scheduler/README.md
+++ b/study/kernel/01-process/05-schedule/06-main_scheduler/README.md
@@ -581,8 +581,41 @@ rev->sched_class == class && rq->nr_running == rq->cfs.h_nr_running
 
 ##context_switch进程上下文切换
 -------
+
+**进程上下文切换**
+
+
+**上下文切换**(有时也称做**进程切换**或**任务切换**)是指CPU从一个进程或线程切换到另一个进程或线程
+
+稍微详细描述一下，上下文切换可以认为是内核（操作系统的核心）在 CPU 上对于进程（包括线程）进行以下的活动：
+
+1.	挂起一个进程，将这个进程在 CPU 中的状态（上下文）存储于内存中的某处，
+
+2.	在内存中检索下一个进程的上下文并将其在 CPU 的寄存器中恢复
+
+3.	跳转到程序计数器所指向的位置（即跳转到进程被中断时的代码行），以恢复该进程
+
+
+上下文是指某一时间点CPU寄存器和程序计数器的内容, 广义上还包括内存中进程的弟子映射信息
+
+上下文切换只能发生在内核态中, 上下文切换通常是计算密集型的。也就是说，它需要相当可观的处理器时间，在每秒几十上百次的切换中，每次切换都需要纳秒量级的时间。所以，上下文切换对系统来说意味着消耗大量的 CPU 时间，事实上，可能是操作系统中时间消耗最大的操作。
+Linux相比与其他操作系统（包括其他类 Unix 系统）有很多的优点，其中有一项就是，其上下文切换和模式切换的时间消耗非常少.
+
+context_switch函数完成了进程上下文的切换, 其定义在[kernel/sched/core.c#L2715](http://lxr.free-electrons.com/source/kernel/sched/core.c#L2715),
 http://abcdxyzk.github.io/blog/2014/05/22/kernel-sched-tick/
 
+执行如下操作
+
+*	调用switch_mm(), 把虚拟内存从一个进程映射切换到新进程中
+
+*	调用switch_to(),从上一个进程的处理器状态切换到新进程的处理器状态。这包括保存、恢复栈信息和寄存器信息 
+
+context_switch( )函数建立next进程的地址空间。进程描述符的active_mm字段指向进程所使用的内存描述符，而mm字段指向进程所拥有的内存描述符。对于一般的进程，这两个字段有相同的地址，但是，内核线程没有它自己的地址空间而且它的 mm字段总是被设置为 NULL
+
+context_switch( )函数保证：如果next是一个内核线程, 它使用prev所使用的地址空间
+
+进程切换并不是我们今天的重点, 我们将在后面的章节中着重讲解
+
 
 ##need_resched与TIF_NEED_RESCHED标识
 -------
diff --git a/study/kernel/01-process/05-schedule/06-main_scheduler/context_switch.c b/study/kernel/01-process/05-schedule/06-main_scheduler/context_switch.c
new file mode 100644
index 0000000..04c3ea2
--- /dev/null
+++ b/study/kernel/01-process/05-schedule/06-main_scheduler/context_switch.c
@@ -0,0 +1,62 @@
+/*
+ * context_switch - switch to the new MM and the new thread's register state.
+ */
+static __always_inline struct rq *
+context_switch(struct rq *rq, struct task_struct *prev,
+           struct task_struct *next)
+{
+    struct mm_struct *mm, *oldmm;
+
+    prepare_task_switch(rq, prev, next);
+
+    mm = next->mm;
+    oldmm = prev->active_mm;
+    /*
+     * For paravirt, this is coupled with an exit in switch_to to
+     * combine the page table reload and the switch backend into
+     * one hypercall.
+     */
+    arch_start_context_switch(prev);
+
+    if (!mm) {
+        next->active_mm = oldmm;
+        atomic_inc(&oldmm->mm_count);
+        enter_lazy_tlb(oldmm, next);
+    } else
+        switch_mm(oldmm, mm, next);
+
+    if (!prev->mm) {
+        prev->active_mm = NULL;
+        rq->prev_mm = oldmm;
+    }
+    /*
+     * Since the runqueue lock will be released by the next
+     * task (which is an invalid locking op but in the case
+     * of the scheduler it's an obvious special-case), so we
+     * do an early lockdep release here:
+     */
+    lockdep_unpin_lock(&rq->lock);
+    spin_release(&rq->lock.dep_map, 1, _THIS_IP_);
+
+    /* Here we just switch the register state and the stack. */
+    switch_to(prev, next, prev);
+    barrier();
+
+    return finish_task_switch(prev);
+}
+
+/*
+ * nr_running and nr_context_switches:
+ *
+ * externally visible scheduler statistics: current number of runnable
+ * threads, total number of context switches performed since bootup.
+ */
+unsigned long nr_running(void)
+{
+    unsigned long i, sum = 0;
+
+    for_each_online_cpu(i)
+        sum += cpu_rq(i)->nr_running;
+
+    return sum;
+}
\ No newline at end of file
diff --git a/study/kernel/01-process/05-schedule/06-main_scheduler/pick_next_task.c b/study/kernel/01-process/05-schedule/06-main_scheduler/pick_next_task.c
index db4bf25..3fd78d2 100644
--- a/study/kernel/01-process/05-schedule/06-main_scheduler/pick_next_task.c
+++ b/study/kernel/01-process/05-schedule/06-main_scheduler/pick_next_task.c
@@ -25,8 +25,8 @@ pick_next_task(struct rq *rq, struct task_struct *prev)
     {
         /*  调用cfs的选择函数pick_next_task找到最优的那个进程p*/
         p = fair_sched_class.pick_next_task(rq, prev);
-        /*  #define RETRY_TASK ((void *)-1UL)没有找到合适的进程  */
-        if (unlikely(p == RETRY_TASK))  
+        /*  #define RETRY_TASK ((void *)-1UL)有被其他调度气找到合适的进程  */
+        if (unlikely(p == RETRY_TASK))
             goto again; /*  则遍历所有的调度器类找到最优的进程 */
 
         /* assumes fair_sched_class->next == idle_sched_class */