From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752696AbZKHMwH (ORCPT ); Sun, 8 Nov 2009 07:52:07 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752624AbZKHMwG (ORCPT ); Sun, 8 Nov 2009 07:52:06 -0500 Received: from mx2.mail.elte.hu ([157.181.151.9]:44955 "EHLO mx2.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752630AbZKHMwE (ORCPT ); Sun, 8 Nov 2009 07:52:04 -0500 Date: Sun, 8 Nov 2009 13:51:35 +0100 From: Ingo Molnar To: Avi Kivity Cc: Gleb Natapov , kvm@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, "H. Peter Anvin" , Thomas Gleixner , Fr??d??ric Weisbecker Subject: Re: [PATCH 02/11] Add "handle page fault" PV helper. Message-ID: <20091108125135.GA13099@elte.hu> References: <1257076590-29559-1-git-send-email-gleb@redhat.com> <1257076590-29559-3-git-send-email-gleb@redhat.com> <20091102092214.GB8933@elte.hu> <20091102160410.GF27911@redhat.com> <20091102161248.GB15423@elte.hu> <20091102162234.GH27911@redhat.com> <20091102162941.GC14544@elte.hu> <20091102174208.GJ27911@redhat.com> <20091108113654.GO11372@elte.hu> <4AF6BCE5.3030701@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4AF6BCE5.3030701@redhat.com> User-Agent: Mutt/1.5.20 (2009-08-17) X-ELTE-SpamScore: 0.0 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=0.0 required=5.9 tests=none autolearn=no SpamAssassin version=3.2.5 _SUMMARY_ Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Avi Kivity wrote: > On 11/08/2009 01:36 PM, Ingo Molnar wrote: > >>Three existing callbacks are: kmemcheck, mmiotrace, notifier. Two > >>of them kmemcheck, mmiotrace are enabled only for debugging, should > >>not be performance concern. And notifier call sites (two of them) > >>are deliberately, as explained by comment, not at the function entry, > >>so can't be unified with others. (And kmemcheck also has two different > >>call site BTW) > > > > We want mmiotrace to be generic distro capable so the overhead when > > the hook is not used is of concern. > > Maybe we should generalize paravirt-ops patching in case if (x) f() is > deemed too expensive. Yes, that's a nice idea. We have quite a number of 'conditional callbacks' in various critical paths that could be made lighter via such a technique. It would also free new callbacks from the 'it increases overhead even if unused' criticism and made it easier to add them. Ingo From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ingo Molnar Subject: Re: [PATCH 02/11] Add "handle page fault" PV helper. Date: Sun, 8 Nov 2009 13:51:35 +0100 Message-ID: <20091108125135.GA13099@elte.hu> References: <1257076590-29559-1-git-send-email-gleb@redhat.com> <1257076590-29559-3-git-send-email-gleb@redhat.com> <20091102092214.GB8933@elte.hu> <20091102160410.GF27911@redhat.com> <20091102161248.GB15423@elte.hu> <20091102162234.GH27911@redhat.com> <20091102162941.GC14544@elte.hu> <20091102174208.GJ27911@redhat.com> <20091108113654.GO11372@elte.hu> <4AF6BCE5.3030701@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Gleb Natapov , kvm@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, "H. Peter Anvin" , Thomas Gleixner , Fr??d??ric Weisbecker To: Avi Kivity Return-path: Content-Disposition: inline In-Reply-To: <4AF6BCE5.3030701@redhat.com> Sender: owner-linux-mm@kvack.org List-Id: kvm.vger.kernel.org * Avi Kivity wrote: > On 11/08/2009 01:36 PM, Ingo Molnar wrote: > >>Three existing callbacks are: kmemcheck, mmiotrace, notifier. Two > >>of them kmemcheck, mmiotrace are enabled only for debugging, should > >>not be performance concern. And notifier call sites (two of them) > >>are deliberately, as explained by comment, not at the function entry, > >>so can't be unified with others. (And kmemcheck also has two different > >>call site BTW) > > > > We want mmiotrace to be generic distro capable so the overhead when > > the hook is not used is of concern. > > Maybe we should generalize paravirt-ops patching in case if (x) f() is > deemed too expensive. Yes, that's a nice idea. We have quite a number of 'conditional callbacks' in various critical paths that could be made lighter via such a technique. It would also free new callbacks from the 'it increases overhead even if unused' criticism and made it easier to add them. Ingo -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org