Tasklet vs workqueues

Hi All, I took following lines from robert love linux kernel development. " If you need a schedulable entity to perform your bottom-half processing, you need work queues.They are the only bottom-half mechanisms that run in process context, and thus, the only ones that can sleep.This means they are useful for situations in which you need to allocate a lot of memory, obtain a semaphore, or perform block I/O. If you do not need a kernel thread to handle your deferred work, consider a tasklet instead ." Here some times tasklets also runs in kernel thread context(by ksoftirqd/n).So I want to know what is the exact difference between workqueue and tasklet. thanks, santosh.