I am a Linux device driver newbie, and want to know the exact differences between tasklet
and workqueue
. I have the following doubts:
- Which kernel stack do interrupts, tasklet and workqueue use when running in interrupt/process context?
- At what priority would tasklet and workqueue run and can we modify it's priority?
- If I implement my own work queue list, can I schedule/prioritize it independently?
Tasklets:
Work queues:
Bottom line is: use tasklets for high priority, low latency atomic tasks that must still execute outside the hard IRQ context.
You can control some level of priority with tasklets using tasklet_hi_enable
/tasklet_hi_schedule
(instead of their respective no-_hi
versions). From this IBM page:
The normal-priority schedule is performed through the TASKLET_SOFTIRQ-level softirq, where high priority is through the HI_SOFTIRQ-level softirq.
...
Tasklets from the high-priority vector are serviced first, followed by those on the normal vector. Note that each CPU maintains its own normal and high-priority softirq vectors.
With work queues, when creating one, you will use alloc_workqueue
(create_workqueue
is deprecated) and can pass a flag to ask for higher priority:
WQ_HIGHPRI:
Work items of a highpri wq are queued to the highpri thread-pool of the target gcwq. Highpri thread-pools are served by worker threads with elevated nice level.
Note that normal and highpri thread-pools don't interact with each other. Each maintain its separate pool of workers and implements concurrency management among its workers.
I cannot answer all your questions, but I hope this helps anyway.