From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757140AbaEIQmd (ORCPT ); Fri, 9 May 2014 12:42:33 -0400 Received: from mga09.intel.com ([134.134.136.24]:52529 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756907AbaEIQmb (ORCPT ); Fri, 9 May 2014 12:42:31 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.97,1019,1389772800"; d="scan'208";a="509110106" Message-ID: <536D0571.6030202@intel.com> Date: Fri, 09 May 2014 09:42:25 -0700 From: Dave Hansen User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.4.0 MIME-Version: 1.0 To: Steven Rostedt CC: Thomas Gleixner , x86@kernel.org, Peter Zijlstra , LKML , Gleb Natapov , Seiji Aguchi , "H. Peter Anvin" Subject: Re: KVM_GUEST support breaks page fault tracing References: <536C039A.5000204@intel.com> <536C0DA8.4090608@intel.com> <20140508194508.561ed220@gandalf.local.home> In-Reply-To: <20140508194508.561ed220@gandalf.local.home> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05/08/2014 04:45 PM, Steven Rostedt wrote: > As your patch showed up as an attachment, I couldn't include it in my > reply. But sure, that may work. But you could also play tricks to keep > the overhead off when tracing is disabled like this one: ... How important is it to have zero-overhead? This bug was introduced by trying to do just that, and I'm worried about having an explosion of so many paths to get in to the page fault code. The overhead in this case is just a few noops, right? I guess that's a question for the KVM folks. Do you guys prefer zero overhead or simpler code?