Tasklet vs workqueues

[santhosh kumars]

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.