linux-kernel - Re: [PATCH v2] kunit: fix failure to build without printk

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Date:   Fri, 30 Aug 2019 16:36:05 -0700
From:   Joe Perches <joe@...ches.com>
To:     Tim.Bird@...y.com, brendanhiggins@...gle.com
Cc:     shuah@...nel.org, sergey.senozhatsky.work@...il.com,
        kunit-dev@...glegroups.com, linux-kernel@...r.kernel.org,
        linux-kselftest@...r.kernel.org, frowand.list@...il.com,
        sboyd@...nel.org, pmladek@...e.com, sergey.senozhatsky@...il.com,
        rostedt@...dmis.org, rdunlap@...radead.org, sfr@...b.auug.org.au
Subject: Re: [PATCH v2] kunit: fix failure to build without printk

On Fri, 2019-08-30 at 23:22 +0000, Tim.Bird@...y.com wrote:
> > -----Original Message-----
> > From: Brendan Higgins 
> > 
> > On Fri, Aug 30, 2019 at 3:46 PM Joe Perches <joe@...ches.com> wrote:
> > > On Fri, 2019-08-30 at 21:58 +0000, Tim.Bird@...y.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.

deduplication can matter as well, but so far
there is little content with kunit_(err|warn|info(=)

kunit/example-test.c:   kunit_info(test, "initializing\n");
kunit/test.c:           kunit_err(test,
kunit/test.c:                   kunit_err(test, "%s", fragment->fragment);
kunit/test.c:           kunit_err(test, "\n");
kunit/test.c:           kunit_err(test, "%s", buf);
kunit/test.c:                   kunit_err(test, "failed to initialize: %d\n", ret);
kunit/test.c:                   kunit_err(test, "test case timed out\n");
kunit/test.c:                   kunit_err(test, "internal error occurred preventing test case from running: %d\n",
kunit/try-catch.c:              kunit_err(test, "try timed out\n");
kunit/try-catch.c:              kunit_err(test, "wake_up_process() was never called\n");
kunit/try-catch.c:              kunit_err(test, "Unknown error: %d\n", exit_code);

Of these, only two do match other kernel uses.

"initializing\n", "failed to initialize: %d\n"