IPI 通信（SMP）【转】

转自：https://winddoing.github.io/post/60164.html

IPI (Interrupt-Procecesorr Interrupt): 处理中间的中断

主要应用是一个处理器让另一个处理器做特定的事情（function 和 sched）

 

              +---------------------------+-+
system boot   | request_percpu_irq（）      +
              | mailbox irq handle          +
              +--+-----------------------+--+
                 |                       |
                 |                       |
              +--v--+                +---v-+
              | CPU0|                > CPU1|
              +--+--+                +----++
                 |                        |
            +----+----+             +-----+-----+
            |mailbox0 |          +-->mailbox1   |
            +---------+          |  +-----------+
                                 |
                 +---------------+        |
system run    A send IPI CPU1             |
              write mailbox1              |
                 |                        |
                 |                  +-----v-----------------+---+
          +------+----+             | 1. 读取mailbox中的action  +
          |  Task A   |             | 2. 通过action判断IPI类型  +
          |           |             | 3. 进行function和sched处理+
          +-----------+             |                           +
                                    +---------------------------+

在多核处理器中，每一个 CPU 核有一个 mailbox(相当于邮箱)，如果需要进行 IPI 通信时，其主要通过 IPI 的中断实现。假设 CPU0 需要给 CPU1 发送一个 action(actionI 的类型：SMP_CALL_FUNCTION,SMP_RESCHEDULE_YOURSELF 等) 时，只需要 CPU0 向 CPU1 的 mailbox 中写于 action 的 id（相当于信），此时 CPU1 将产生一个 IPI 中断（表明收到信），mailbox 的中断处理程序将读取 mailbox（相当于看信）中的 action，判断 action 的类型进行相应的处理。

MIPS 架构下的 IPI 通信

1. 关闭中断后还会发送 IPI

MIPS 接口

 

struct plat_smp_ops {
	void (*send_ipi_single)(int cpu, unsigned int action);
	void (*send_ipi_mask)(const struct cpumask *mask, unsigned int action);
	...
}

IPI 通信就是多个处理器之间的交流。
send_ipi_single： 一对一聊天
send_ipi_mask : 群发，mask 表示群发的成员（CPU）

action 类型

 

/* Octeon - Tell another core to flush its icache */

/* Used by kexec crashdump to save all cpu's state */

file: arch/mips/include/asm/smp.h

1. 不同的 action (活动) 何时将产生？
2. 各自都有什么作用？

SMP_RESCHEDULE_YOURSELF

SMP_RESCHEDULE_YOURSELF 将直接调用 scheduler_ipi. 将任务插入目标 CPU 的运行队列。

 

/*
 * this function sends a 'reschedule' IPI to another CPU.
 * it goes straight through and wastes no time serializing
 * anything. Worst case is that we lose a reschedule ...
 */
static inline void smp_send_reschedule(int cpu)
{
	extern struct plat_smp_ops *mp_ops; /* private */

	mp_ops->send_ipi_single(cpu, SMP_RESCHEDULE_YOURSELF);
}

file: arch/mips/include/asm/smp.h

SMP_CALL_FUNCTION

SMP_CALL_FUNCTION: 将特定的函数在目标 CPU 上运行

• 内核回调接口：
   

static inline void arch_send_call_function_single_ipi(int cpu)
{
	extern struct plat_smp_ops *mp_ops; /* private */

	mp_ops->send_ipi_mask(&cpumask_of_cpu(cpu), SMP_CALL_FUNCTION);
}

static inline void arch_send_call_function_ipi_mask(const struct cpumask *mask)
{
	extern struct plat_smp_ops *mp_ops; /* private */

	mp_ops->send_ipi_mask(mask, SMP_CALL_FUNCTION);
}

file: arch/mips/include/asm/smp.h

 

/*
 * smp_call_function_single - Run a function on a specific CPU
 * @func: The function to run. This must be fast and non-blocking.
 * @info: An arbitrary pointer to pass to the function.
 * @wait: If true, wait until function has completed on other CPUs.
 *
 * Returns 0 on success, else a negative status code.
 */

smp_call_function_single
	->generic_exec_single
		->arch_send_call_function_single_ipi

/**
 * smp_call_function_many(): Run a function on a set of other CPUs.
 * @mask: The set of cpus to run on (only runs on online subset).
 * @func: The function to run. This must be fast and non-blocking.
 * @info: An arbitrary pointer to pass to the function.
 * @wait: If true, wait (atomically) until function has completed
 *        on other CPUs.
 *
 * If @wait is true, then returns once @func has returned.
 *
 * You must not call this function with disabled interrupts or from a
 * hardware interrupt handler or from a bottom half handler. Preemption
 * must be disabled when calling this function.
 */

smp_call_function_many
	->arch_send_call_function_ipi_mask

file: kernel/smp.c

刷新 TLB

多核进行 TLB 的同步？