Re: DPC vs tasklet

[Jeff Garzik <jgarzik@pobox.com>]

Infante, Jon wrote:
> Christoph,
> 
> I was going to take your advice:
> "usage of tasklet itself is questionable, you probably want a kernel-thread"
> 
> and redo our driver bottom half discovery handler to use a DPC. I just
> wanted to get your opinion of why usage of a tasklet is questionable. Some
> of the LINUX documentation I've read states "tasklets are the preferred
> mechanism with which to implement your bottom half for a normal hardware
> device". I can see, as you stated, being in user context will help with
> things like allowing the use of GFP_KERNEL for memory allocations or safe
> calling of del_timer_sync(); but its not real clear to me what all the
> tradeoffs are and why some people think tasklets are the preferred
> mechanism. Can you shed some more light on this or direct me to some URLs
> with more info.


There are tradeoffs.  Using a kernel thread increases latency, and is 
not always the best choice.

It really depends on how much "work" you need to do in the interrupt 
handling and bottom-half phases.

If we are talking per-irq or per-IO, kernel thread is a poor choice.

	Jeff