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

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Date:   Mon, 12 Nov 2018 14:30:01 -0800
From:   Joe Perches <joe@...ches.com>
To:     Dave Chinner <david@...morbit.com>,
        Eric Sandeen <sandeen@...deen.net>
Cc:     "Darrick J. Wong" <darrick.wong@...cle.com>,
        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 Tue, 2018-11-13 at 08:45 +1100, Dave Chinner wrote:
> On Mon, Nov 12, 2018 at 02:12:08PM -0600, Eric Sandeen wrote:
> > On 11/10/18 7:21 PM, Joe Perches wrote:
> > > Reduce total object size quite a bit (~32KB) and presumably
> > > improve performance at the same time.
> > > 
> > > Total object size old vs new (x86-64 defconfig with xfs)
> > > 
> > >     text	   data	    bss	    dec	    hex	filename
> > > - 959351	 165573	    632	1125556	 112cb4	(TOTALS) (old)
> > > + 924683	 165669	    632	1090984	 10a5a8	(TOTALS) (new)
> > 
> > And what does it do to maximum stack excursions?
> 
> Better yet: what does it do to corruption stack traces and debugging
> tools like profiling traces?
> 
> i.e. this noinline directive isn't about stack usage, this is about
> being able to debug production code. Basically the compiler inliner
> is so agressive on static functions that it makes it impossible to
> decipher the stack traces. It flattens them way too much to
> be able to tell how we got to a specific location in the code.
> 
> In reality, being able to find problems quickly and efficiently is
> far more important to us than being able to run everything at
> ludicrous speed....

Is that really a compelling argument given thw ~50:50
split of static/STATIC uses in xfs?

$ git grep -w STATIC fs/xfs/ | wc -l
1064
$ git grep -w static fs/xfs/ | wc -l
942