On Mon, 10 Jun 2013, Steven Rostedt wrote: > > and why so many drivers > > > are using tasklet/softirq? > > Because it's easy to set up and device driver authors don't know any > better ;-). Note, a lot of drivers are now using work queues today, > which run as a task. > > Yes, there's a little more overhead with a task than for a softirq, but > the problem with softirqs and tasklets is that they can't be preempted, > and they are more important than all tasks on the system. If you have a > task that is critical, it must yield for your softirq. Almost! > > That is, even if you have a softirq, it may not run in irq context at > all. If you get too many softirqs at a time (one comes while another one > is running), it will defer the processing to the ksoftirq thread. This > not only runs as a task, but also runs as SCHED_OTHER, and must yield to > other tasks like everyone else too. > > Thus, adding it as a softirq does not guarantee that it will be > processed quickly. It just means that most of the time it will prevent > anything else from happening while your "most important handler in the > world" is running. >From this, it sounds like you generally advise using threaded interrupt handlers rather than tasklets/softirqs. Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
