From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail143.messagelabs.com (mail143.messagelabs.com [216.82.254.35]) by kanga.kvack.org (Postfix) with ESMTP id 488BB6B004D for ; Sun, 8 Nov 2009 11:47:18 -0500 (EST) Date: Sun, 8 Nov 2009 17:47:06 +0100 From: Ingo Molnar Subject: Re: [PATCH 02/11] Add "handle page fault" PV helper. Message-ID: <20091108164706.GB3286@elte.hu> References: <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> <20091108125135.GA13099@elte.hu> <4AF6F57C.6060706@zytor.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4AF6F57C.6060706@zytor.com> Sender: owner-linux-mm@kvack.org To: "H. Peter Anvin" Cc: Avi Kivity , Gleb Natapov , kvm@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Thomas Gleixner , Fr??d??ric Weisbecker List-ID: * H. Peter Anvin wrote: > On 11/08/2009 04:51 AM, Ingo Molnar wrote: > > > > * 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. > > There are a number of other things were we permanently bind to a > single instance of something, too. Optimizing those away would be > nice. Consider memcpy(), where we may want to have different > implementations for different processors. yeah. 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