From mboxrd@z Thu Jan 1 00:00:00 1970 From: Kyle McMartin Subject: Re: [PATCH] btrfs: fix __ucmpdi2 compile bug on 32 bit builds Date: Sun, 29 Mar 2009 15:22:03 -0400 Message-ID: <20090329192203.GF29999@bombadil.infradead.org> References: <20090327134252.0f24773b@osiris.boeblingen.de.ibm.com> <87prg26l79.fsf@basil.nowhere.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Heiko Carstens , Chris Mason , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org To: Andi Kleen Return-path: Received: from bombadil.infradead.org ([18.85.46.34]:40482 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752862AbZC2TWO (ORCPT ); Sun, 29 Mar 2009 15:22:14 -0400 Content-Disposition: inline In-Reply-To: <87prg26l79.fsf@basil.nowhere.org> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On Sat, Mar 28, 2009 at 10:38:50AM +0100, Andi Kleen wrote: > To be honest that sounds more like a bug in your architecture. > > I don't think it's the right solution to make a new rule > "you shall not do 64bit switch()", because that's a reasonable > thing to do and will be hard to enforce over millions of lines > of random Linux code. > > There was a explicit decision to not support implicit 64bit > divides on 32bit because they're very costly, but that doesn't > really apply to 64bit switch(). At least they shouldn't be very costly > in theory. It seems indeed weird to call a function to compare > a 64bit value. I bet the call sequence is larger than just > doing two cmps. Perhaps your gcc should be fixed? Or alternatively > at least that function be added to the kernel runtime library. > i386 will do this kind of stupidity too if you let it. I had to fix this in nouveau a few weeks back because they were doing a u64 modulus (a power of 2 too, no idea why gcc was so clueless as to not properly reduce it...) GCC is getting much worse in this regard... regards, Kyle