From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.1 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 46899C43441 for ; Wed, 10 Oct 2018 10:18:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id BF14B214FF for ; Wed, 10 Oct 2018 10:18:58 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=armlinux.org.uk header.i=@armlinux.org.uk header.b="MpHEcJTU" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org BF14B214FF Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=armlinux.org.uk Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726616AbeJJRkZ (ORCPT ); Wed, 10 Oct 2018 13:40:25 -0400 Received: from pandora.armlinux.org.uk ([78.32.30.218]:46292 "EHLO pandora.armlinux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725827AbeJJRkZ (ORCPT ); Wed, 10 Oct 2018 13:40:25 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=armlinux.org.uk; s=pandora-2014; h=Sender:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=WdzpGAe1GfXOVXBpxadD7R70TRb1Ea3ietdzXlqfnck=; b=MpHEcJTUO9f1S9DhclxWQ/vhJ i8wktpHPal4rD/NbEmIBbKWBdbEf8dQizLrvEFkt6rk9rqYQaLYo6h9GFQAkZ9I6HM14CmKqebrMf 5PuqhN9Lv+F6nRKJMgAXXyXmdnarPp/NiXbKRhgJuPWPqn/7fY3IPqk1bet8uFGUFoZ7A=; Received: from n2100.armlinux.org.uk ([fd8f:7570:feb6:1:214:fdff:fe10:4f86]:39988) by pandora.armlinux.org.uk with esmtpsa (TLSv1.2:ECDHE-RSA-AES128-GCM-SHA256:128) (Exim 4.90_1) (envelope-from ) id 1gABZk-00068F-M6; Wed, 10 Oct 2018 11:18:44 +0100 Received: from linux by n2100.armlinux.org.uk with local (Exim 4.90_1) (envelope-from ) id 1gABZi-0000XQ-0i; Wed, 10 Oct 2018 11:18:42 +0100 Date: Wed, 10 Oct 2018 11:18:40 +0100 From: Russell King - ARM Linux To: Will Deacon Cc: Peter Zijlstra , corbet@lwn.net, b.zolnierkie@samsung.com, linux-kernel@vger.kernel.org, Lukasz Luba , mingo@redhat.com, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH] Doc: lockdep: add information about performance impact Message-ID: <20181010101840.GM30658@n2100.armlinux.org.uk> References: <20181009153935eucas1p2dec146575ed5fefd4a0b2b6cb9bac056~b_ujkjRd31303013030eucas1p2C@eucas1p2.samsung.com> <20181009154359.GB5728@hirez.programming.kicks-ass.net> <20181009155818.GD9259@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181009155818.GD9259@arm.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Oct 09, 2018 at 04:58:18PM +0100, Will Deacon wrote: > On Tue, Oct 09, 2018 at 05:43:59PM +0200, Peter Zijlstra wrote: > > On Tue, Oct 09, 2018 at 05:39:27PM +0200, Lukasz Luba wrote: > > > This patch add some warning related to performance drop. > > > It should be mentioned that this is not for free > > > and the platfrom resources (cache, bus interconnect, etc.) > > > will be used more frequently. > > > > To me this reads a bit like: water is wet. > > > > Is this really needed? > > I don't think so -- this is a debug option under "kernel hacking". Surely > the perf hit comes with the territory. Indeed it does - since adding debug code means additional instructions, more cache pressure and, therefore, slower execution. I've already said to people... turn on all debug options for development, and when you move to performance evaluation and optimisation for the production version, evaluate and turn off debug options. Unfortunately, turning off PROVE_LOCKING in the defconfigs is going to have a negative impact on the automated build/boot testing that systems like kernelci.org do for us - these are primarily based around the defconfigs, which means we're going to end up building with PROVE_LOCKING disabled. This means kernelci.org will be less likely to catch locking issues. Forcing PROVE_LOCKING on also doesn't make sense - there may be (rare) bugs, eg race conditions, uncovered by having that disabled. -- RMK's Patch system: http://www.armlinux.org.uk/developer/patches/ FTTC broadband for 0.8mile line in suburbia: sync at 12.1Mbps down 622kbps up According to speedtest.net: 11.9Mbps down 500kbps up From mboxrd@z Thu Jan 1 00:00:00 1970 From: linux@armlinux.org.uk (Russell King - ARM Linux) Date: Wed, 10 Oct 2018 11:18:40 +0100 Subject: [PATCH] Doc: lockdep: add information about performance impact In-Reply-To: <20181009155818.GD9259@arm.com> References: <20181009153935eucas1p2dec146575ed5fefd4a0b2b6cb9bac056~b_ujkjRd31303013030eucas1p2C@eucas1p2.samsung.com> <20181009154359.GB5728@hirez.programming.kicks-ass.net> <20181009155818.GD9259@arm.com> Message-ID: <20181010101840.GM30658@n2100.armlinux.org.uk> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Tue, Oct 09, 2018 at 04:58:18PM +0100, Will Deacon wrote: > On Tue, Oct 09, 2018 at 05:43:59PM +0200, Peter Zijlstra wrote: > > On Tue, Oct 09, 2018 at 05:39:27PM +0200, Lukasz Luba wrote: > > > This patch add some warning related to performance drop. > > > It should be mentioned that this is not for free > > > and the platfrom resources (cache, bus interconnect, etc.) > > > will be used more frequently. > > > > To me this reads a bit like: water is wet. > > > > Is this really needed? > > I don't think so -- this is a debug option under "kernel hacking". Surely > the perf hit comes with the territory. Indeed it does - since adding debug code means additional instructions, more cache pressure and, therefore, slower execution. I've already said to people... turn on all debug options for development, and when you move to performance evaluation and optimisation for the production version, evaluate and turn off debug options. Unfortunately, turning off PROVE_LOCKING in the defconfigs is going to have a negative impact on the automated build/boot testing that systems like kernelci.org do for us - these are primarily based around the defconfigs, which means we're going to end up building with PROVE_LOCKING disabled. This means kernelci.org will be less likely to catch locking issues. Forcing PROVE_LOCKING on also doesn't make sense - there may be (rare) bugs, eg race conditions, uncovered by having that disabled. -- RMK's Patch system: http://www.armlinux.org.uk/developer/patches/ FTTC broadband for 0.8mile line in suburbia: sync at 12.1Mbps down 622kbps up According to speedtest.net: 11.9Mbps down 500kbps up