Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933112AbXK2To6 (ORCPT ); Thu, 29 Nov 2007 14:44:58 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1757719AbXK2Top (ORCPT ); Thu, 29 Nov 2007 14:44:45 -0500 Received: from mx3.mail.elte.hu ([157.181.1.138]:34787 "EHLO mx3.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757325AbXK2Too (ORCPT ); Thu, 29 Nov 2007 14:44:44 -0500 Date: Thu, 29 Nov 2007 20:44:16 +0100 From: Ingo Molnar To: Andi Kleen Cc: "H. Peter Anvin" , Linus Torvalds , Andi Kleen , Chuck Ebbert , Roland McGrath , Andrew Morton , linux-kernel@vger.kernel.org, Thomas Gleixner , Jeremy Fitzhardinge , zach@vmware.com Subject: Re: [PATCH x86/mm 6/6] x86-64 ia32 ptrace get/putreg32 current task Message-ID: <20071129194416.GB15245@elte.hu> References: <20071129003849.428E026F8E7@magilla.localdomain> <20071129004222.E49AD26F8E7@magilla.localdomain> <474EF824.3020806@redhat.com> <474F01F6.2030509@zytor.com> <474F08E1.2090806@zytor.com> <474F1027.2020801@zytor.com> <20071129192721.GP24223@one.firstfloor.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20071129192721.GP24223@one.firstfloor.org> User-Agent: Mutt/1.5.17 (2007-11-01) X-ELTE-VirusStatus: clean X-ELTE-SpamScore: -1.5 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-1.5 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.2.3 -1.5 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1047 Lines: 24 * Andi Kleen wrote: > For i386 iirc Jeremy/Zach did the benchmarking and they settled on %fs > because it was faster for something (originally it was %gs too) yep. IIRC, some CPUs only optimize %fs because that's what Windows uses and leaves Linux with %gs out in the cold. There's also a performance penalty for overlapping segment use, if the segment cache is single entry only with an additional optimization for NULL [which just hides the segment cache]. But if it's good for unification we could switch that to %gs again on 32-bit. I was one of the people who advocated the use of the 'other' segment register, so that the hardware has less overlap, but clean and unified code trumps this concern. It shouldnt be an issue on reasonably modern CPUs anyway. Ingo - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/