Linux软中断实现详解(2.6.26.3)

软中断的类型：

enum { HI_SOFTIRQ=0, TIMER_SOFTIRQ, NET_TX_SOFTIRQ, NET_RX_SOFTIRQ, BLOCK_SOFTIRQ, TASKLET_SOFTIRQ, SCHED_SOFTIRQ, #ifdef CONFIG_HIGH_RES_TIMERS HRTIMER_SOFTIRQ, #endif RCU_SOFTIRQ, /* Preferable RCU should always be the last softirq */ };

关键数据结构和函数介绍：

in_interrupt()函数：

#define in_interrupt() (irq_count()) #define irq_count() (preempt_count() & (HARDIRQ_MASK | SOFTIRQ_MASK )) #define preempt_count() (current_thread_info()->preempt_count) #define SOFTIRQ_MASK (__IRQ_MASK(SOFTIRQ_BITS) << SOFTIRQ_SHIFT) #define HARDIRQ_MASK (__IRQ_MASK(HARDIRQ_BITS) << HARDIRQ_SHIFT) #define NMI_MASK (__IRQ_MASK(NMI_BITS) << NMI_SHIFT) #define __IRQ_MASK(x) ((1UL << (x))-1) #define PREEMPT_BITS 8 #define SOFTIRQ_BITS 8 #define HARDIRQ_BITS 12 #define PREEMPT_SHIFT 0 #define SOFTIRQ_SHIFT (PREEMPT_SHIFT + PREEMPT_BITS) #define HARDIRQ_SHIFT (SOFTIRQ_SHIFT + SOFTIRQ_BITS)

 

可见，宏in_interrupt()检查当前进程thread_info结构中的preempt_count字段中硬中断和软中断计数器，其全为0，才返回0.

preempt_count字段的含义：

0-7:抢占计数器，记录显示禁用本地CPU内核抢占的次数，值等于0表示允许内核抢占。

8-15:表示软中断被禁用的程度，同样值为0表示处于激活状态。

16-27：表示本地CPU中断处理程序的嵌套数。

表示软中断的主要数据结构为softirq_action类型的数组，数组名为softirq_vec。

 

01.struct softirq_action 02.{ 03. void (*action)(struct softirq_action *); 04. void *data; 05.}; 06.static struct softirq_action softirq_vec[32] __cacheline_aligned_in_smp; 

另外一个实现软中断的数据结构是irq_cpustat_t。

01.typedef struct { 02. unsigned int __softirq_pending; 03. unsigned long idle_timestamp; 04. unsigned int __nmi_count; /* arch dependent */ 05. unsigned int apic_timer_irqs; /* arch dependent */ 06. unsigned int irq0_irqs; 07. unsigned int irq_resched_count; 08. unsigned int irq_call_count; 09. unsigned int irq_tlb_count; 10. unsigned int irq_thermal_count; 11. unsigned int irq_spurious_count; 12.} ____cacheline_aligned irq_cpustat_t;