RE: [PATCH v2] kunit: fix failure to build without printk

Tim.Bird
2019-08-30T23:23:06Z

> -----Original Message-----
> From: Brendan Higgins
>
> On Fri, Aug 30, 2019 at 3:46 PM Joe Perches <joe@perches.com> wrote:
> >
> > On Fri, 2019-08-30 at 21:58 +0000, Tim.Bird@sony.com wrote:
> > > > From: Joe Perches
> > []
> > > IMHO %pV should be avoided if possible. Just because people are
> > > doing it doesn't mean it should be used when it is not necessary.
> >
> > Well, as the guy that created %pV, I of course
> > have a different opinion.
> >
> > > > then wouldn't it be easier to pass in the
> > > > > kernel level as a separate parameter and then strip off all printk
> > > > > headers like this:
> > > >
> > > > Depends on whether or not you care for overall
> > > > object size. Consolidated formats with the
> > > > embedded KERN_<LEVEL> like suggested are smaller
> > > > overall object size.
> > >
> > > This is an argument I can agree with. I'm generally in favor of
> > > things that lessen kernel size creep. :-)
> >
> > As am I.
>
> Sorry, to be clear, we are talking about the object size penalty due
> to adding a single parameter to a function. Is that right?

Not exactly. The argument is that pre-pending the different KERN_LEVEL
strings onto format strings can result in several versions of nearly identical strings
being compiled into the object file. By parameterizing this (that is, adding
'%s' into the format string, and putting the level into the string as an argument),
it prevents this duplication of format strings.

I haven't seen the data on duplication of format strings, and how much this
affects it, but little things can add up. Whether it matters in this case depends
on whether the format strings that kunit uses are also used elsewhere in the kernel,
and whether these same format strings are used with multiple kernel message levels.
-- Tim