From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1945894AbXC2W2f (ORCPT ); Thu, 29 Mar 2007 18:28:35 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1945895AbXC2W2f (ORCPT ); Thu, 29 Mar 2007 18:28:35 -0400 Received: from emailhub.stusta.mhn.de ([141.84.69.5]:38066 "EHLO mailhub.stusta.mhn.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1945894AbXC2W2e (ORCPT ); Thu, 29 Mar 2007 18:28:34 -0400 Date: Fri, 30 Mar 2007 00:28:32 +0200 From: Adrian Bunk To: =?utf-8?B?Si5BLiBNYWdhbGzDs24=?= Cc: "Linux-Kernel, " Subject: Re: Inlining can be _very_bad... Message-ID: <20070329222832.GE14134@stusta.de> References: <20070329011838.6e832615@werewolf-wl> <20070329175254.GC14134@stusta.de> <20070330000111.620aaaab@werewolf-wl> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20070330000111.620aaaab@werewolf-wl> User-Agent: Mutt/1.5.13 (2006-08-11) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Mar 30, 2007 at 12:01:11AM +0200, J.A. Magallón wrote: > On Thu, 29 Mar 2007 19:52:54 +0200, Adrian Bunk wrote: > > > On Thu, Mar 29, 2007 at 01:18:38AM +0200, J.A. Magallón wrote: > > > Hi all... > > > > > > I post this here as it can be of direct interest for kernel development > > > (as I recall many discussions about inlining yes or no...). > > > > > > Testing other problems, I finally got this this issue: the same short > > > and stupid loop lasted from 3 to 5 times more if it was in main() than > > > if it was in an out-of-line function. The same (bad thing) happens if > > > the function is inlined. > > >... > > > It looks like is updating the stack on each iteration...This is -march=opteron > > > code, the -march=pentium4 is similar. Same behaviour with gcc3 and gcc4. > > > > > > tst.c and Makefile attached. > > > > > > Nice, isn't it ? Please, probe where is my fault... > > > > The only fault is to post this issue here instead of the gcc Bugzilla. > > Sorry, my intention was just something like 'take a look at your > reduction-like code, perhaps its sloooow', something like checksum > funtions in tcp or raid that are inlined expecting to be faster > and in fact they are slower... Unless a function that has more than 1 caller is very tiny or reduces at compile time to a very tiny rest, it's not expected that inlining was faster on current CPUs. But most times that's already only up to the compiler - e.g. current gcc versions already automatically inline all static functions with only 1 caller. > > In your example the compiler should produce code not slower than with > > the out-of-line version when inlining. If it doesn't the bug in the > > compiler resulting in this should be fixed. > > That's what I expected, but... > Going to gcc bugzilla... Thanks. cu Adrian -- "Is there not promise of rain?" Ling Tan asked suddenly out of the darkness. There had been need of rain for many days. "Only a promise," Lao Er said. Pearl S. Buck - Dragon Seed