From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753134Ab1JQSux (ORCPT ); Mon, 17 Oct 2011 14:50:53 -0400 Received: from mx2.mail.elte.hu ([157.181.151.9]:47854 "EHLO mx2.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751221Ab1JQSuw (ORCPT ); Mon, 17 Oct 2011 14:50:52 -0400 Date: Mon, 17 Oct 2011 20:49:18 +0200 From: Ingo Molnar To: Thomas Gleixner Cc: Linus Torvalds , Simon Kirby , Peter Zijlstra , Linux Kernel Mailing List , Dave Jones , Martin Schwidefsky Subject: Re: Linux 3.1-rc9 Message-ID: <20111017184916.GA5545@elte.hu> References: <20111007070842.GA27555@hostway.ca> <20111007174848.GA11011@hostway.ca> <1318010515.398.8.camel@twins> <20111008005035.GC22843@hostway.ca> <1318060551.8395.0.camel@twins> <20111012213555.GC24461@hostway.ca> <20111013232521.GA5654@hostway.ca> <20111017045806.GA11561@elte.hu> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) X-ELTE-SpamScore: -2.0 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-2.0 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.3.1 -2.0 BAYES_00 BODY: Bayes spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Thomas Gleixner wrote: > > That simple time type could then trickle down as well: we could > > use it everywhere in kernel code and limit the hodge-podge of ABI > > time units to the syscall boundary. (and convert the internal > > time unit to whatever ABI unit there is close to the syscall > > boundary) > > > > There's a point where micro-optimized 32-bit support related > > maintenance overhead (and the resulting loss of > > robustness/flexibility) becomes too expensive IMO. > > That's not a micro optimization, it's a massive performance hit if > you force those 32bit archs to do 64/32 all over the place. Do we have some hard data on this, which we could put into comments in include/linux/ktime.h and such? Older versions of GCC used to do a bad job of long long handling on 32-bit systems - that might be a factor in the performance figures. But i suspect you are right that the cost is still very much there ... Thanks, Ingo