Queries on bottom halves

[greg@kroah.com (Greg KH)]

On Sun, Sep 02, 2018 at 01:39:07PM -0400, valdis.kletnieks at vt.edu wrote:
> On Sun, 02 Sep 2018 20:58:14 +0530, Abhinav Misra said:
> 
> > But if in new kernel this implementation is changed then why we need so
> > many options to defer the work as all of them are basically getting
> > executed in almost the same way.* In that case code running softirq,
> > tasklet, workqueue and kernel thread are all same ?*
> > If this is true then why we just remove all these these option and keep one
> > or two alternative.
> 
> -ENOPATCH
> 
> Often the gain from simplification isn't enough to motivate somebody to
> actually do all the work of coding and exhaustively testing the patch series.

Also, when switching to a different mechanism (or combining them), odd
things happen due to the fact that those different methods do work just
a little bit differently.

This was recently shown by some noticable slowdowns in some USB device
paths like cameras, when one low-level primative in one subsystem moved
from one type to another to try to "simplify" things.

So Valdis is right, the only way this could ever be done is if someone
does the work.  And it's a lot of non-trivial work to do...

greg k-h