What are Tasklets in Linux?

What are Tasklets in Linux?

Tasklet in Linux Kernel Tasklets are used to queue up work to be done at a later time. Tasklets can be run in parallel, but the same tasklet cannot be run on multiple CPUs at the same time. In short, a tasklet in linux is something like a very small thread that has neither stack, not the context of its own.

What is Softirq and Tasklets?

Generally speaking, softirqs are re-entrant functions and must explicitly protect their data structures with spin locks. Tasklets differ from softirqs because a tasklet is always serialized with respect to itself; in other words, a tasklet cannot be executed by two CPUs at the same time.

What is the difference between Workqueue and Tasklet?

A tasklet always runs in the interrupt context, that means when a tasklet executes it is as if the processor is executing an interrupt service routine. On the other hand a workqueue executes as a normal process and not a interrupt, hence a worqueue can go to sleep it can hold semaphores.

What is Tasklet kernel?

Tasklets are a deferral scheme that you can schedule for a registered function to run later. The top half (the interrupt handler) performs a small amount of work, and then schedules the tasklet to execute later at the bottom half.

When should I use Tasklets?

1) The Tasklet are used in interrupt context. All the tasklet code must be atomic,so all rules that are applied on atomic context are applied to it. For eg. They cannot sleep(as they cannot be reschecduled) or hold a lock for long time.

Can Tasklets be interrupted?

It is possible and even common that a tasklet will disable interrupts during short critical sections while it manipulates shared data structures.

What is a Linux Softirq?

SoftIrqs allow the critical part of servicing hardware interrupts to be as short as possible; instead of having to process the entire hw interrupt on the spot, the important data is read off the device into RAM or otherwise, and then a SoftIrq is started to finish the work.

Is it safe to use semaphore in Tasklet?

As with softirqs, tasklets cannot sleep. This means you cannot use semaphores or other blocking functions in a tasklet. Tasklets also run with all interrupts enabled, so you must take precautions (for example, disable interrupts and obtain a lock) if your tasklet shares data with an interrupt handler.

What is Workqueue in Linux?

A “workqueue” is a list of tasks to perform, along with a (per-CPU) kernel thread to execute those tasks. Since a kernel thread is used, all tasks are run in process context and may safely sleep.

What is a tasklet in Linux?

Tasklets are built on top of softirqs to allow dynamic creation of deferrable functions. Finally, in the 2.5 Linux kernel, work queues were introduced (see ./include/linux/workqueue.h). Work queues permit work to be deferred outside of the interrupt context into the kernel process context.

What Linux kernel version are Tasklets and work queues?

This discussion of tasklets and work queues uses the 2.6.27.14 version of the Linux kernel. Linux tends to be a Swiss Army knife of functionality, and deferring functionality is no different. Since kernel 2.3, softirqs have been available that implement a set of 32 statically defined bottom halves.

When does a tasklet get scheduled?

A tasklet is a softirq and hence runs in an interrupt context. Thus while executing the function you are not allowed to go to sleep and have to use proper locking for any data that is shared with other tasklets. When does the tasklet actually get scheduled can not be controlled and is decided by the scheduler depending on the load on the processor.

Can a tasklet run on multiple cores?

A tasklet only runs on the same core (CPU) that schedules it. Different tasklets can be running in parallel. But at the same time, a tasklet cannot be called concurrently with itself, as it runs on one CPU only. Tasklets are executed by the principle of non-preemptive scheduling, one by one, in turn.