From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754168AbYHVOp2 (ORCPT ); Fri, 22 Aug 2008 10:45:28 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752101AbYHVOpU (ORCPT ); Fri, 22 Aug 2008 10:45:20 -0400 Received: from bombadil.infradead.org ([18.85.46.34]:45471 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751560AbYHVOpU (ORCPT ); Fri, 22 Aug 2008 10:45:20 -0400 Date: Fri, 22 Aug 2008 10:45:16 -0400 From: Christoph Hellwig To: Arjan van de Ven Cc: Andrew Morton , linux-kernel@vger.kernel.org, mingo@elte.hu Subject: Re: PATCH] debug: add notifier chain debugging Message-ID: <20080822144516.GA12479@infradead.org> References: <20080815152938.4bc9d48c@infradead.org> <20080819210932.9bb348b9.akpm@linux-foundation.org> <20080822070054.5d466be9@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20080822070054.5d466be9@infradead.org> User-Agent: Mutt/1.5.18 (2008-05-17) X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org See http://www.infradead.org/rpr.html Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Aug 22, 2008 at 07:00:54AM -0700, Arjan van de Ven wrote: > On Tue, 19 Aug 2008 21:09:32 -0700 > Andrew Morton wrote: > > > > > If we remove the first two checks then surely we can afford to add the > > remaining check unconditionally and lose the new config option and its > > ifdef. > > > > Andi told me that this notifier is a hotpath for kprobes (systemtap) > use models; at which point making this a config option makes sort of > sense to get the last bit of performance out of that. Personally I would > always want this option on for anything I run, and I suspect > (enterprise) distros will just always turn it on as well since it's a > good sanity check at low cost. > > I'd be happy to lose the config (I think we have way too many unneeded > ones of those already); I'll make a patch. What about checking yourself? At least the braindead use of notiiers in the pagefault path for kprobes (even unconditional on x86_64) is gone now and replaced with proper kprobes hooks. The die notifier that's also used by kprobes shouldn't be in a performance critical path.