From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1764028AbZFOTP1 (ORCPT ); Mon, 15 Jun 2009 15:15:27 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752011AbZFOTPR (ORCPT ); Mon, 15 Jun 2009 15:15:17 -0400 Received: from terminus.zytor.com ([198.137.202.10]:50767 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751104AbZFOTPQ (ORCPT ); Mon, 15 Jun 2009 15:15:16 -0400 Message-ID: <4A369CD8.3090505@zytor.com> Date: Mon, 15 Jun 2009 12:11:20 -0700 From: "H. Peter Anvin" User-Agent: Thunderbird 2.0.0.21 (X11/20090320) MIME-Version: 1.0 To: Peter Zijlstra CC: Mathieu Desnoyers , Linus Torvalds , Ingo Molnar , mingo@redhat.com, paulus@samba.org, acme@redhat.com, linux-kernel@vger.kernel.org, penberg@cs.helsinki.fi, vegard.nossum@gmail.com, efault@gmx.de, jeremy@goop.org, npiggin@suse.de, tglx@linutronix.de, linux-tip-commits@vger.kernel.org Subject: Re: [tip:perfcounters/core] perf_counter: x86: Fix call-chain support to use NMI-safe methods References: <20090615171845.GA7664@elte.hu> <4A369508.2090707@zytor.com> <20090615184858.GD6520@Krystal> <1245091917.6741.185.camel@laptop> <20090615185907.GF6520@Krystal> <1245092561.6741.205.camel@laptop> In-Reply-To: <1245092561.6741.205.camel@laptop> 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 Peter Zijlstra wrote: > On Mon, 2009-06-15 at 14:59 -0400, Mathieu Desnoyers wrote: >> * Peter Zijlstra (a.p.zijlstra@chello.nl) wrote: >>> On Mon, 2009-06-15 at 14:48 -0400, Mathieu Desnoyers wrote: >>>> we should not care that much about the performance hit of >>>> saving/restoring the cr2 register at each nmi entry/exit. >>> But we do, perf counters very much cares about nmi performance. >>> >> To a point where it cannot afford a simple register save/restore ? >> >> There is "caring" and "_caring_". I am tempted to ask what NMI handler >> execution frequency you have in mind here to figure out if we are not >> trying to optimize sub-nanoseconds per minutes. ;) > > Ah, well, I have no idea who expensive cr2 is, if its like a regular > register then it should be fine. If however its tons more expensive then > we should really avoid it. > > As to the freq, 100kHz would be nice ;-) > Writing control registers is serializing, so it's a lot more expensive than writing a normal register; my *guess* is that it will be on the order of 100-200 cycles. That is not based on any actual information. -hpa