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From: <Tim.Bird@sony.com>
To: <brendanhiggins@google.com>
Cc: <joe@perches.com>, <shuah@kernel.org>,
	<sergey.senozhatsky.work@gmail.com>, <kunit-dev@googlegroups.com>,
	<linux-kernel@vger.kernel.org>, <linux-kselftest@vger.kernel.org>,
	<frowand.list@gmail.com>, <sboyd@kernel.org>, <pmladek@suse.com>,
	<sergey.senozhatsky@gmail.com>, <rostedt@goodmis.org>,
	<rdunlap@infradead.org>, <sfr@canb.auug.org.au>
Subject: RE: [PATCH v2] kunit: fix failure to build without printk
Date: Sat, 31 Aug 2019 00:06:32 +0000
Message-ID: <ECADFF3FD767C149AD96A924E7EA6EAF977A846B@USCULXMSG01.am.sony.com> (raw)
In-Reply-To: <20190830233710.GA101591@google.com>

> -----Original Message-----
> From: Brendan Higgins 
> 
> On Fri, Aug 30, 2019 at 11:22:43PM +0000, Tim.Bird@sony.com wrote:
> > > -----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
> 
> I thought this portion of the discussion was about whether Joe's version
> of kunit_printk was better or my critique of his version of kunit_printk:
> 
> Joe's:
> > > > > -void kunit_printk(const char *level,
> > > > > -		  const struct kunit *test,
> > > > > -		  const char *fmt, ...)
> > > > > +void kunit_printk(const struct kunit *test, const char *fmt, ...)
> > > > >  {
> > > > > +	char lvl[PRINTK_MAX_SINGLE_HEADER_LEN + 1] = "\0";
> > > > >  	struct va_format vaf;
> > > > >  	va_list args;
> > > > > +	int kern_level;
> > > > >
> > > > >  	va_start(args, fmt);
> > > > >
> > > > > +	while ((kern_level = printk_get_level(fmt)) != 0) {
> > > > > +		size_t size = printk_skip_level(fmt) - fmt;
> > > > > +
> > > > > +		if (kern_level >= '0' && kern_level <= '7') {
> > > > > +			memcpy(lvl, fmt,  size);
> > > > > +			lvl[size] = '\0';
> > > > > +		}
> > > > > +		fmt += size;
> > > > > +	}
> > > > > +
> > > > >  	vaf.fmt = fmt;
> > > > >  	vaf.va = &args;
> > > > >
> > > > > -	kunit_vprintk(test, level, &vaf);
> > > > > +	printk("%s\t# %s %pV\n", lvl, test->name, &vaf);
> > > > >
> > > > >  	va_end(args);
> > > > >  }
> 
> Mine:
> >  void kunit_printk(const char *level,
> >  		  const struct kunit *test,
> >  		  const char *fmt, ...)
> >  {
> >  	struct va_format vaf;
> >  	va_list args;
> >
> >  	va_start(args, fmt);
> >
> > +	fmt = printk_skip_headers(fmt);
> > +
> >  	vaf.fmt = fmt;
> >  	vaf.va = &args;
> >
> > -	kunit_vprintk(test, level, &vaf);
> > +	printk("%s\t# %s %pV\n", level, test->name, &vaf);
> >
> >  	va_end(args);
> >  }
> 
> I thought you and Joe were arguing that "Joe's" resulted in a smaller
> object size than "Mine" (not to be confused with the actual patch I
> presented here, which is what Sergey suggested I do on a different
> thread).
> 
> I really don't feel strongly about what Sergey suggested I do (which is
> what this patch originally introduced), versus, what Joe suggested,
> versus what I suggested in response to Joe (or any of the things
> suggested on other threads). I just want to pick one, fix the breakage
> in linux-next, and move on with my life.

When in doubt, do what the sub-system maintainer says.  I'd go
with Sergey's suggestion.  Maintainers often are juggling a host
of issues, and weighing new features and usages of their system
against their long-term plans for their sub-system.  Sometimes
they have time to communicate all the intricacies of their
counter-proposals, and sometimes not.

But they know their system best, and much more often than not
provide sound advice.

If you don't have a strong feeling about it, just do what they
say.
 -- Tim


  parent reply index

Thread overview: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-28  9:31 Brendan Higgins
2019-08-28  9:49 ` Sergey Senozhatsky
2019-08-28 11:50   ` Petr Mladek
2019-08-29 17:01   ` shuah
2019-08-30  4:44     ` Joe Perches
2019-08-30  4:56       ` Joe Perches
2019-08-30 18:38       ` Brendan Higgins
2019-08-30 20:46         ` Joe Perches
2019-08-30 21:58           ` Tim.Bird
2019-08-30 22:46             ` Joe Perches
2019-08-30 23:02               ` Brendan Higgins
2019-08-30 23:22                 ` Tim.Bird
2019-08-30 23:36                   ` Joe Perches
2019-08-30 23:37                   ` Brendan Higgins
2019-08-30 23:43                     ` Joe Perches
2019-08-31  0:06                     ` Tim.Bird [this message]
2019-09-02 12:52                     ` Petr Mladek
2019-09-02 14:39                       ` shuah
2019-08-30 23:29               ` Tim.Bird
2019-08-30  5:19     ` Sergey Senozhatsky
2019-08-28 15:52 ` Randy Dunlap

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