From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755274AbZCHWMm (ORCPT ); Sun, 8 Mar 2009 18:12:42 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753800AbZCHWMd (ORCPT ); Sun, 8 Mar 2009 18:12:33 -0400 Received: from mx3.mail.elte.hu ([157.181.1.138]:51510 "EHLO mx3.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753521AbZCHWMc (ORCPT ); Sun, 8 Mar 2009 18:12:32 -0400 Date: Sun, 8 Mar 2009 23:12:08 +0100 From: Ingo Molnar To: "H. Peter Anvin" Cc: Jeremy Fitzhardinge , Andrew Morton , the arch/x86 maintainers , Linux Kernel Mailing List , Xen-devel Subject: Re: [PATCH] xen: core dom0 support Message-ID: <20090308221208.GA24079@elte.hu> References: <1235786365-17744-1-git-send-email-jeremy@goop.org> <20090227212812.26d02f34.akpm@linux-foundation.org> <20090228084254.GA29342@elte.hu> <49A907DD.6010408@goop.org> <20090302120859.GB29015@elte.hu> <49B23907.8030103@goop.org> <20090308110150.GA19151@elte.hu> <49B43F1D.2000400@zytor.com> <20090308220609.GA23447@elte.hu> <49B441D9.4010004@zytor.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <49B441D9.4010004@zytor.com> User-Agent: Mutt/1.5.18 (2008-05-17) 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 List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * H. Peter Anvin wrote: > Ingo Molnar wrote: > > > > Since it's the same kernel image i think the only truly reliable > > method would be to reboot between _different_ kernel images: > > same instructions but randomly re-align variables both in terms > > of absolute address and in terms of relative position to each > > other. Plus randomize bootmem allocs and never-gets-freed-really > > boot-time allocations. > > > > Really hard to do i think ... > > > > Ouch, yeah. > > On the other hand, the numbers made sense to me, so I don't > see why there is any reason to distrust them. They show a 5% > overhead with pv_ops enabled, reduced to a 2% overhead with > the changed. That is more or less what would match my > intuition from seeing the code. Yeah - it was Jeremy expressed doubt in the numbers, not me. And we need to eliminate that 2% as well - 2% is still an awful lot of native kernel overhead from a kernel feature that 95%+ of users do not make any use of. Ingo From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ingo Molnar Subject: Re: [PATCH] xen: core dom0 support Date: Sun, 8 Mar 2009 23:12:08 +0100 Message-ID: <20090308221208.GA24079@elte.hu> References: <1235786365-17744-1-git-send-email-jeremy@goop.org> <20090227212812.26d02f34.akpm@linux-foundation.org> <20090228084254.GA29342@elte.hu> <49A907DD.6010408@goop.org> <20090302120859.GB29015@elte.hu> <49B23907.8030103@goop.org> <20090308110150.GA19151@elte.hu> <49B43F1D.2000400@zytor.com> <20090308220609.GA23447@elte.hu> <49B441D9.4010004@zytor.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <49B441D9.4010004@zytor.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: "H. Peter Anvin" Cc: Xen-devel , Jeremy Fitzhardinge , the arch/x86 maintainers , Andrew Morton , Linux Kernel Mailing List List-Id: xen-devel@lists.xenproject.org * H. Peter Anvin wrote: > Ingo Molnar wrote: > > > > Since it's the same kernel image i think the only truly reliable > > method would be to reboot between _different_ kernel images: > > same instructions but randomly re-align variables both in terms > > of absolute address and in terms of relative position to each > > other. Plus randomize bootmem allocs and never-gets-freed-really > > boot-time allocations. > > > > Really hard to do i think ... > > > > Ouch, yeah. > > On the other hand, the numbers made sense to me, so I don't > see why there is any reason to distrust them. They show a 5% > overhead with pv_ops enabled, reduced to a 2% overhead with > the changed. That is more or less what would match my > intuition from seeing the code. Yeah - it was Jeremy expressed doubt in the numbers, not me. And we need to eliminate that 2% as well - 2% is still an awful lot of native kernel overhead from a kernel feature that 95%+ of users do not make any use of. Ingo