c - What is the difference between tasklet and workqueue -

i linux device driver newbie, , want know exact differences between tasklet , workqueue. additionally have following doubts too:

1. which kernel stack interrupts, tasklet , workqueue use when running in interrupt/process context?
2. at priority tasklet , workqueue run , can modify it's priority?
3. if implement own work queue list, can schedule/prioritize independently?

tasklets:

• are old (around 2.3 believe)
• have straightforward, simple api
• are designed low latency
• cannot sleep (run atomically in soft irq context , guaranteed never run on more 1 cpu of given processor, given tasklet)

work queues:

• are more recent (introduced in 2.5)
• have flexible api (more options/flags supported)
• are designed higher latency
• can sleep

bottom line is: use tasklets high priority, low latency atomic tasks must still execute outside hard irq context.

you can control level of priority tasklets using tasklet_hi_enable/tasklet_hi_schedule (instead of respective no-_hi versions). this ibm page:

the normal-priority schedule performed through tasklet_softirq-level softirq, high priority through hi_softirq-level softirq.

...

tasklets high-priority vector serviced first, followed on normal vector. note each cpu maintains own normal , high-priority softirq vectors.

with work queues, when creating one, use alloc_workqueue (create_workqueue deprecated) , can pass flag ask higher priority:

wq_highpri:

work items of highpri wq queued highpri thread-pool of target gcwq. highpri thread-pools served worker threads elevated nice level.

note normal , highpri thread-pools don't interact each other. each maintain separate pool of workers , implements concurrency management among workers.

i cannot answer questions, hope helps anyway.