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=-6.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED 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 2533EC64EB8 for ; Tue, 9 Oct 2018 17:29:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D4FB621502 for ; Tue, 9 Oct 2018 17:29:38 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D4FB621502 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com 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 S1726564AbeJJAri convert rfc822-to-8bit (ORCPT ); Tue, 9 Oct 2018 20:47:38 -0400 Received: from mx1.redhat.com ([209.132.183.28]:40506 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726415AbeJJArh (ORCPT ); Tue, 9 Oct 2018 20:47:37 -0400 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id E17AF3082E02; Tue, 9 Oct 2018 17:29:36 +0000 (UTC) Received: from llong.remote.csb (dhcp-17-55.bos.redhat.com [10.18.17.55]) by smtp.corp.redhat.com (Postfix) with ESMTP id 130CB78565; Tue, 9 Oct 2018 17:29:35 +0000 (UTC) Subject: Re: [PATCH] lib/Kconfig.debug: add a comment to PROVE_LOCKING impact To: Lukasz Luba , linux-kernel@vger.kernel.org Cc: b.zolnierkie@samsung.com, mingo@redhat.com References: <20181009153959eucas1p1ab3c10ba4868a4e97a1bff24d8f34c41~b_u5xrZ3z3130331303eucas1p1U@eucas1p1.samsung.com> From: Waiman Long Organization: Red Hat Message-ID: Date: Tue, 9 Oct 2018 13:29:35 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.2.0 MIME-Version: 1.0 In-Reply-To: <20181009153959eucas1p1ab3c10ba4868a4e97a1bff24d8f34c41~b_u5xrZ3z3130331303eucas1p1U@eucas1p1.samsung.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8BIT Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.46]); Tue, 09 Oct 2018 17:29:36 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/09/2018 11:39 AM, Lukasz Luba wrote: > This patch add some comment related to performance impact, > which can be really big (x3 times slower context switch). > > Signed-off-by: Lukasz Luba > --- > lib/Kconfig.debug | 11 +++++++++++ > 1 file changed, 11 insertions(+) > > diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug > index 4966c4f..9e67a2a3 100644 > --- a/lib/Kconfig.debug > +++ b/lib/Kconfig.debug > @@ -1088,6 +1088,9 @@ config PROVE_LOCKING > the proof of observed correctness is also maintained for an > arbitrary combination of these separate locking variants. > > + This feature enables LOCKDEP which can harm system performance > + even x3 times. > + > For more details, see Documentation/locking/lockdep-design.txt. > > config LOCK_STAT > @@ -1112,6 +1115,10 @@ config LOCK_STAT > CONFIG_LOCK_STAT defines "contended" and "acquired" lock events. > (CONFIG_LOCKDEP defines "acquire" and "release" events.) > > + This feature enables LOCKDEP which can harm system performance > + even x3 times. > + For more details, see Documentation/locking/lockdep-design.txt. > + > config DEBUG_RT_MUTEXES > bool "RT Mutex debugging, deadlock detection" > depends on DEBUG_KERNEL && RT_MUTEXES > @@ -1175,6 +1182,10 @@ config DEBUG_LOCK_ALLOC > spin_lock_init()/mutex_init()/etc., or whether there is any lock > held during task exit. > > + This feature enables LOCKDEP which can harm system performance > + even x3 times. > + For more details, see Documentation/locking/lockdep-design.txt. > + > config LOCKDEP > bool > depends on DEBUG_KERNEL && LOCK_DEBUGGING_SUPPORT I don't mind seeing warning message about the performance impact of enabling lockdep. However, the actual slowdown depends on many factors including the type of systems, workloads and so on. I am a bit hesitant to quote an actual figure like x3 in the help text as it may not be correct in many cases. BTW, my recent lockdep patch (https://lkml.org/lkml/2018/10/2/1410) should be able to reduce the performance impact of enabling lockdep. Could you try to see if that help in your case? Cheers, Longman