Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750727AbVK3AwV (ORCPT ); Tue, 29 Nov 2005 19:52:21 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750737AbVK3AwV (ORCPT ); Tue, 29 Nov 2005 19:52:21 -0500 Received: from ozlabs.org ([203.10.76.45]:45952 "EHLO ozlabs.org") by vger.kernel.org with ESMTP id S1750727AbVK3AwV (ORCPT ); Tue, 29 Nov 2005 19:52:21 -0500 Date: Wed, 30 Nov 2005 11:52:05 +1100 From: David Gibson To: Andi Kleen Cc: Nicholas Miell , Stephane Eranian , Ray Bryant , discuss@x86-64.org, linux-kernel@vger.kernel.org, perfctr-devel@lists.sourceforge.net Subject: Re: [Perfctr-devel] Re: Enabling RDPMC in user space by default Message-ID: <20051130005205.GD9659@localhost.localdomain> Mail-Followup-To: David Gibson , Andi Kleen , Nicholas Miell , Stephane Eranian , Ray Bryant , discuss@x86-64.org, linux-kernel@vger.kernel.org, perfctr-devel@lists.sourceforge.net References: <1133300591.3271.1.camel@entropy> <20051129215207.GR19515@wotan.suse.de> <1133303615.3271.12.camel@entropy> <20051129224346.GS19515@wotan.suse.de> <1133305338.3271.30.camel@entropy> <20051129231750.GU19515@wotan.suse.de> <1133306966.3271.36.camel@entropy> <20051129233920.GW19515@wotan.suse.de> <20051129235626.GC9659@localhost.localdomain> <20051130003433.GA19515@wotan.suse.de> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20051130003433.GA19515@wotan.suse.de> User-Agent: Mutt/1.5.9i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1459 Lines: 32 On Wed, Nov 30, 2005 at 01:34:33AM +0100, Andi Kleen wrote: > On Wed, Nov 30, 2005 at 10:56:26AM +1100, David Gibson wrote: > > On Wed, Nov 30, 2005 at 12:39:20AM +0100, Andi Kleen wrote: > > > > Well, if that's all you want them to use RDPMC 0 for, why not just make > > > > PMCs programmable from userspace? > > > > > > First we need to have a cycle counter PMC anyways for the NMI watchdog. > > > So it can as well be used for other purposes. > > > > But the watchdog doesn't require it to be in the same place on all > > machines. Exporting it turns an internal requirement into an ABI > > point. > > Yes, but the only alternative I know of would be to let user space > continue getting broken all the time with RDTSC. RDPMC is a nice > alternative. It just seems to me unwise to make an ABI commitment to something that's not guaranteed by the architecture, perverse though it might seem for the chip designers to take it away. CPU designers have been known to do some fairly perverse things from time to time.. -- David Gibson | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_ | _way_ _around_! http://www.ozlabs.org/~dgibson - 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/