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

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Date:   Tue, 13 Nov 2018 14:09:26 +1100
From:   Dave Chinner <david@...morbit.com>
To:     "Theodore Y. Ts'o" <tytso@....edu>, Joe Perches <joe@...ches.com>,
        Eric Sandeen <sandeen@...deen.net>,
        "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 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...

> functions.  Now, ext4 generally only has about 3 or 4 nested inlines,
> and so I don't know how it works with 20 or 30 nested inlined
> functions, so perhaps this is not applicable for XFS.
> 
> But it perhaps toolchain technology has advanced since the Irix days
> such that it's no longer as necessary to force the non-inlining of
> functions for easing debugging?

Not that I've noticed.

Indeed, modern toolchains are moving the opposite direction - have
you ever tried to debug a binary with gdb that was compiled with LTO
enabled? Or maybe even just tried to profile it with perf?

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com