linux-kernel - Re: [PATCH] xfs: Remove noinline from #define STATIC

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Date:   Mon, 12 Nov 2018 21:44:48 -0800
From:   "Darrick J. Wong" <darrick.wong@...cle.com>
To:     Joe Perches <joe@...ches.com>
Cc:     Dave Chinner <david@...morbit.com>,
        "Theodore Y. Ts'o" <tytso@....edu>,
        Eric Sandeen <sandeen@...deen.net>,
        Christoph Hellwig <hch@....de>, linux-xfs@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] xfs: Remove noinline from #define STATIC

On Mon, Nov 12, 2018 at 09:31:51PM -0800, Joe Perches wrote:
> On Tue, 2018-11-13 at 16:26 +1100, Dave Chinner wrote:
> > On Mon, Nov 12, 2018 at 08:23:42PM -0800, Joe Perches wrote:
> > > On Tue, 2018-11-13 at 14:09 +1100, Dave Chinner wrote:
> > > > On Mon, Nov 12, 2018 at 08:54:10PM -0500, Theodore Y. Ts'o wrote:
> > > > > On Tue, Nov 13, 2018 at 12:18:05PM +1100, Dave Chinner wrote:
> > > > > > I'm not interested in making code fast if distro support engineers
> > > > > > can't debug problems on user systems easily. Optimising for
> > > > > > performance over debuggability is a horrible trade off for us to
> > > > > > make because it means users and distros end up much more reliant on
> > > > > > single points of expertise for debugging problems. And that means
> > > > > > the majority of the load of problem triage falls directly on very
> > > > > > limited resources - the core XFS development team. A little bit of
> > > > > > thought about how to make code easier to triage and debug goes a
> > > > > > long, long way....
> > > > > 
> > > > > So at least in my experience, if the kernels are compiled with
> > > > > CONFIG_DEBUG_INFO and/or CONFIG_DEBUG_INFO_REDUCED,
> > > > > scripts/decode_stracktrace.sh seems to do a very nice job with inlined
> > > > 
> > > > That doesn't help with kernel profiling and other such things that
> > > > are based on callgraphs...
> > > 
> > > If that's really the case:
> > > 
> > > I rather suspect the xfs static v STATIC function marking is not
> > > particularly curated and the marking is somewhat arbitrary.

I disagree.  I've added plenty of code over the past couple of years.
Short functions with few or no branches (e.g. converters) are 'static';
longer functions (loops, iterators, "decide what to do with this"
functions, etc.) with many branches are STATIC to make it easier for me
to ftrace their decisions over a given dataset.

> > That's a common opinion for an outsider to form when they come
> > across something unfamiliar they don't really understand. "I don't
> > understand this, so I must rewrite it" is an unfortunate habit that
> > programmers have.
> 
> Silly.

Yet frequent.

> > > So perhaps given the large number of static, but not STATIC
> > > functions, perhaps a sed of s/static/STATIC/ should be done
> > > when it's not inline for all xfs functions.
> > 
> > That's just as bad as removing them all, if not worse. 
> 
> Why?
> 
> > If you are writing new code or reworking existing code, then we'll
> > consider the usage of STATIC/static in the context of that work.
> > Otherwise, we leave it alone.
> 
> If your statement is as described above, and
> the STATIC use to enable call stack tracing i
> useful, why shouldn't it be systemic?
> 
> > It if ain't broke, don't fix it.
> 
> A generically lazy statement.

Please everyone let's take a breather from this thread for a few hours.
A 3.7% reduction in code size is not worth getting worked up over, IMO.

--D

> 
>