From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1765194AbZFOTDP (ORCPT ); Mon, 15 Jun 2009 15:03:15 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755960AbZFOTDA (ORCPT ); Mon, 15 Jun 2009 15:03:00 -0400 Received: from casper.infradead.org ([85.118.1.10]:33668 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754462AbZFOTC7 (ORCPT ); Mon, 15 Jun 2009 15:02:59 -0400 Subject: Re: [tip:perfcounters/core] perf_counter: x86: Fix call-chain support to use NMI-safe methods From: Peter Zijlstra To: Mathieu Desnoyers Cc: "H. Peter Anvin" , 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 In-Reply-To: <20090615185907.GF6520@Krystal> References: <20090615171845.GA7664@elte.hu> <4A369508.2090707@zytor.com> <20090615184858.GD6520@Krystal> <1245091917.6741.185.camel@laptop> <20090615185907.GF6520@Krystal> Content-Type: text/plain Date: Mon, 15 Jun 2009 21:02:41 +0200 Message-Id: <1245092561.6741.205.camel@laptop> Mime-Version: 1.0 X-Mailer: Evolution 2.26.1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 ;-)