On 12 Oct 2009, at 6:24 AM, Joel Fernandes wrote:
Hi Friends, I have a question about tasklets: I understand that they are used to defer work during interrupt handling. What I don't understand is - how do they handle queuing of deferred work? Specially with tasklets, if a tasklet is re-scheduled before the previous scheduling of the same tasklet has a chance to run, then the tasklet is executed only once - not twice. But what if the work that the tasklet was supposed to do in these 2 instances were different and that its function was supposed to be passed 2 different structures? Shouldn't the tasklet be executed twice with these 2 structures? I know that work queues are there for that, but how do device drivers that use tasklets cope with the above?
The tasklet_schedule() function takes only the struct tasklet_struct* as parameter, so no extra information is sent to the tasklet function. That struct is typically initialized only once, taking the function pointer and one opaque value as parameters. The opaque value will typically point to a device specific struct. The tasklet function needs to infer all the information it requires just from the fact that it has been called (meaning one or more interrupts occurred, if it was scheduled from an interrupt handler), and e.g. read status registers etc. to determine what to do. You _could_ probably push values onto an atomic list or fifo in the interrupt handler and pop them off in a loop in the tasklet, but I don't think that is the recommended way. It also seems from some lwn.net articles that tasklets might be going away in the near future, to be replaced with threaded interrupts.
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