Gentoo Archives: gentoo-performance

From: "Douglas Breault Jr." <GenKreton@×××××××.net>
To: gentoo-performance@l.g.o
Cc: ckingsley@×××××.com
Subject: Re: [gentoo-performance] inline considered harmful
Date: Thu, 22 Jul 2004 06:17:49
Message-Id: 20040722021623.230298ad.GenKreton@comcast.net
In Reply to: Re: [gentoo-performance] inline considered harmful by Colin Kingsley
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 > > > > > > > > > > > > > > > > > > > > > > -- > > > gentoo-performance@g.o mailing list > > > > > > > > > > > -- > gentoo-performance@g.o mailing list >

Replies

Subject Author
Re: [gentoo-performance] inline considered harmful Colin Kingsley <ckingsley@×××××.com>