Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755731Ab2FWSZp (ORCPT ); Sat, 23 Jun 2012 14:25:45 -0400 Received: from mga09.intel.com ([134.134.136.24]:36818 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755057Ab2FWSZo (ORCPT ); Sat, 23 Jun 2012 14:25:44 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.67,352,1309762800"; d="scan'208";a="157470058" Message-ID: <4FE60A26.30109@linux.intel.com> Date: Sat, 23 Jun 2012 11:25:42 -0700 From: "H. Peter Anvin" User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:12.0) Gecko/20120430 Thunderbird/12.0.1 MIME-Version: 1.0 To: Arjan van de Ven CC: Steven Rostedt , Hagen Paul Pfeifer , Linus Torvalds , Ingo Molnar , linux-kernel@vger.kernel.org, Peter Zijlstra , Arnaldo Carvalho de Melo , Thomas Gleixner , Andrew Morton Subject: Re: [GIT PULL] perf fixes References: <20120622133650.GA24136@gmail.com> <20120622183827.GA8014@virgo.local> <20120622190632.GB8014@virgo.local> <1340394896.27036.258.camel@gandalf.stny.rr.com> <86448d73-2e19-416f-8104-ce72aa5d76eb@email.android.com> <1340407123.27036.265.camel@gandalf.stny.rr.com> <4FE51325.8090408@linux.intel.com> In-Reply-To: <4FE51325.8090408@linux.intel.com> Content-Type: text/plain; charset=ISO-8859-15 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 921 Lines: 23 On 06/22/2012 05:51 PM, Arjan van de Ven wrote: > > if it's truely an official nop, it will take decoder bandwidth obviously > (which can decode 3 to 4 instructions per cycle, depending on the > brand/model of CPU and the total size in bytes of these instructions). > likewise, at the end of the out of order pipeline, NOPs may take a > retirement slot (again 3 to 4 instructions per cycle) > > icache is there as well, and if the NOP actually changes cpu flags (some > of the less fortunate ones do) that can create a false data dependency. > If it changes CPU flags it's most definitely not a NOP. Either way, the 0F 1F ops are official, and listed in the SDM. -hpa -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/