linux tasklet 4

引用 2 楼 cokeliu 的回复:
谢谢! 请问是否每调用一次tasklet_schedule(B task); B task任务被加到链表上只会被执行一次?
是的，只被加一次
第一次tasklet_schedule(B task)给他一个状态TASK_STATE_SCHED
作标记，以后的tasklet_schedule(B task)会检查这个标记
http://os.inf.tu-dresden.de/l4env/doc/html/dde_linux/group__mod__softirq.html
Deferred Activities
[Linux DDE Common
]
This module emulates deferred activities
at interrupt level inside the Linux kernel.
More...
Softirqs
This is from include/linux/interrupt.h
Softirqs are multithreaded, not serialized BH-like activities. Several
softirqs may run on several CPUs simultaneously - no matter if they are
of the same type.
Properties:
If raise_softirq()
is called, then softirq is guarenteed to be executed on this CPU.
On schedule()
do_softirq() is called if any softirq is active on this CPU.
Softirqs are not serialized in any way.
Linux (2.4.20) has only 4 softirqs:
HI_SOFTIRQ

NET_TX_SOFTIRQ
and NET_RX_SOFTIRQ

TASKLET_SOFTIRQ

Relevant for Linux DDE are for now only the first and the latter - NET_*
softirqs allow transparent mutli-threading in Linux' network code. HI_SOFTIRQ
is for high priority bottom halves as old-style
BHs and sound related drivers. It triggers execution of tasklet_hi_action()
. TASKLET_SOFTIRQ
runs lower priority bottom halves (e.g. in the console subsystem). It triggers execution of tasklet_action()
.
Todo:
only the implementation of tasklets is done in Linux DDE
void 
raise_softirq
(int nr)
 
Raise Softirq.
Tasklets
This is from kernel/softirq.c and include/linux/interrupt.h)
Tasklets are the multithreaded analogue of BHs.
Main feature differing them of generic softirqs: one tasklet is running only on one CPU simultaneously.
Main feature differing them of BHs: different tasklets may be run simultaneously on different CPUs.
Properties:
If tasklet_schedule()
is called, then tasklet is guaranteed to be executed on some cpu at least on