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SubjectRe: [PATCH] ring_buffer: fix ring_buffer_event_length()
On Thu, 8 Jan 2009 12:55:30 +0100 Ingo Molnar <mingo@elte.hu> wrote:

>
> * Andrew Morton <akpm@linux-foundation.org> wrote:
>
> > On Wed, 7 Jan 2009 23:58:39 -0500 (EST) Steven Rostedt <rostedt@goodmis.org> wrote:
> >
> > > kernel/trace/ring_buffer.c | 8 +++++++-
> >
> > <looks>
> >
> > heavens, what a lot of inlining. Looks like something from 1997 :)
> >
> > Prove me wrong!
> >
> >
> > From: Andrew Morton <akpm@linux-foundation.org>
> >
> > text data bss dec hex filename
> > before: 11320 228 8 11556 2d24 kernel/trace/ring_buffer.o
> > after: 10592 228 8 10828 2a4c kernel/trace/ring_buffer.o
>
> You are wrong :-)

Not.

> With x86 defconfig and gcc 4.3.2 i get zero change in size:

With my config and my gcc I see a large change in size. So those
`inline' statements in that C file are *wrong*.

> kernel/trace/ring_buffer.o:
>
> text data bss dec hex filename
> 11485 228 8 11721 2dc9 ring_buffer.o.before
> 11485 228 8 11721 2dc9 ring_buffer.o.after
>
> md5:
> 55447563cd459bbb02c6234b2544fcc2 ring_buffer.o.before.asm
> 55447563cd459bbb02c6234b2544fcc2 ring_buffer.o.after.asm
>
> (i took out the free_page() bit to only measure the inlining)
>
> That is the same with and without CONFIG_OPTIMIZE_INLINING - i.e. recent
> GCC gets the inlining right.
>
> Really, we should stop bothering about inlines on the source code level
> (the kernel has 20,000 inlines and around 100,000 functions - do we really
> want to maintain inlining information on a per function basis?) - and we
> should tell the GCC folks when the compiler messes up some detail.
>
> Or if GCC messes up inlining so much in the future that we cannot live
> with it, we can go back to "always inline" and manual annotations again.
> Or write a new compiler. (the latter is probably less work ;-)

None of that makes the inline statements in ring_buffer.c less wrong.
It says that with some configs and some gcc versions, their damage is
lessened.



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