Linux Device Drivers Development

Tasklets

Tasklets are a bottom-half (we will see what this means later) mechanism built on top of softirqs. They are represented in the kernel as instances of the struct tasklet_struct:

struct tasklet_struct 
{ 
    struct tasklet_struct *next; 
    unsigned long state; 
    atomic_t count; 
    void (*func)(unsigned long); 
    unsigned long data; 
}; 

Tasklets are not re-entrant by nature. Code is called reentrant if it can be interrupted anywhere in the middle of its execution, and then be safely called again. Tasklets are designed such that a tasklet can run on one and only one CPU simultaneously (even on an SMP system), which is the CPU it was scheduled on, but different tasklets may be run simultaneously on different CPUs. The tasklet API is quite basic and intuitive. ...