Re: [gentoo-performance] inline considered harmful

[Douglas Breault Jr.]

There is an fno-inline but i believe it is even more drastic, and I personally try to avoid conflicting settings, I don't trust it to always be bug free. Also to consider for compile time options are fno-default-inline.

I'd like to see some benchmarks before I set these. It doesn't seem like something that would cause errors though. 

On Thu, 22 Jul 2004 01:44:36 -0400
Colin Kingsley <ckingsley@×××××.com> wrote:

> true, you could, but it would be much neater to use -O3 and disable
> stuff using -fno-whatever. Also, this would have the benefit of
> remaining usefull even if a new version of gcc had a diferent set of
> optimisations in -O3.
>
> but thats just my oppinion:)
>
>
>
> On Wed, 21 Jul 2004 21:16:43 -0400, Douglas Breault Jr.
> <genkreton@×××××××.net> wrote:
> > You could just enable -O2 and the following: -frename-registers and -fweb. -O3 is simply -O2 plus those 3 options.
> >
> >
> >
> > On Wed, 21 Jul 2004 20:50:01 -0400
> > Adam Petaccia <adam@×××××××××.com> wrote:
> >
> > > With gcc, is there a way to enable all -O3 options but function
> > > inlines?  Would -fno-inline work or something like that?
> > >
> > > Mario Domenech Goulart wrote:
> > >
> > > >Hello,
> > > >
> > > >There's an interesting discussion in the OpenBSD mailing
> > > >list about the use of inline.
> > > >
> > > >Here's the beginning of the thread about this topic:
> > > >
> > > >,----[ http://www.sigmasoft.com/cgi-bin/wilma_hiliter/openbsd-tech/200407/msg00175.html ]
> > > >| inline considered harmful.
> > > >|
> > > >|     * To: tech@×××××××.org
> > > >|     * Subject: inline considered harmful.
> > > >|     * From: Artur Grabowski <art@××××××××.org>
> > > >|     * Date: 21 Jul 2004 03:54:46 +0200
> > > >|     * User-agent: Gnus/5.09 (Gnus v5.9.0) Emacs/21.2
> > > >|
> > > >| Today we did a bunch of removal of inline functions in the kernel.
> > > >| It all started to make floppies fit, but now it's a quest.
> > > >|
> > > >| If you think that I'm crazy doing this because it might hurt your
> > > >| precious performance, go back to your vax and leave the performance
> > > >| tuning to people who have a cache.
> > > >|
> > > >| Every single inline we removed today (and there are more in the
> > > >| pipeline and even more waiting to be fixed) shrunk the code and MADE
> > > >| IT FASTER.  Yes, modern cpus have something called "cache". The cache
> > > >| prefers the code to be smaller, rather than free from function calls.
> > > >| Yes, some cpus have expensive function call overhead. Don't use them.
> > > >| i386 has quite expensive function calls, on the other hand it doesn't
> > > >| have any relevant amount of registers either. So a function call
> > > >| instead of the same function inlined can potentially make the job
> > > >| easier for the register allocator in the compiler which could eat the
> > > >| overhead. At the same time the instruction cache can run the same code
> > > >| in the same place, instead of loading it from main memory 4711 times.
> > > >| And guess what? The stack on i386 is in the cache too, so the function
> > > >| call overhead isn't that bad anyway.
> > > >|
> > > >| I'm tired of seeing code where everything is made inline just because
> > > >| someone acted on a meme that hasn't been true for over a decade. Bloat,
> > > >| bloat and more bloat. Since people can't use inline correctly (it does
> > > >| have valid and correct uses), from now on inline in the OpenBSD kernel
> > > >| is considered to be a bug until proven otherwise. So. Next time I see
> > > >| code that adds to the bloat with inlines, I expect performance figures
> > > >| and kernel size comparisons that show that the inline actually
> > > >| contributes anything. Otherwise the code does not go in.
> > > >|
> > > >| There's still a lot of work to be done in the kernel (yes, macros can
> > > >| be evil too, just see nfs), so send diffs. And there's a whole
> > > >| unexplored field in userland too.
> > > >|
> > > >| //art
> > > >`----
> > > >
> > > >Mario
> > > >
> > > >
> > > >--
> > > >gentoo-performance@g.o mailing list
> > > >
> > > >
> > > >
> > > >
> > >
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> > >
> >
> >
> >
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