Re: Scheduling tasklets from process context...

[Roland Dreier <roland@topspin.com>]

    arun> Since tasklets are typically used for bottom half
    arun> processing, is it acceptable/recommended that they be
    arun> scheduled from a process context (say an ioctl handler)?

    arun> Should one try to minimize such scheduling and try to do
    arun> things in process context if possible, as tasklets run in
    arun> interrupt context? Or is the driver writer free to use the
    arun> tasklets at will? What is recommended here?

I guess it would work to schedule a tasklet from your ioctl handler, but
I don't see a good reason to do it.  What are you really trying to do?

Your ioctl handler runs in process context so you are free to do
pretty much anything -- allocate with GFP_KERNEL, sleep, etc.  If you
want to return to userspace immediately but defer some work until
later, it would probably make more sense to use something like
schedule_work() instead of a tasklet.

The main point of tasklets is that they run at a high priority, very
soon after they're scheduled, so that an interrupt handler can return
quickly by deferring work to a tasklet but still not add too much
latency.  But in your ioctl handler, if you have some high priority
work, you can just do it immediately without the complication of a tasklet.

 - R.