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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8721CC004D4 for ; Sat, 21 Jan 2023 11:29:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229667AbjAUL3v (ORCPT ); Sat, 21 Jan 2023 06:29:51 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48026 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229523AbjAUL3s (ORCPT ); Sat, 21 Jan 2023 06:29:48 -0500 Received: from smtp-out2.suse.de (smtp-out2.suse.de [IPv6:2001:67c:2178:6::1d]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C38F93B3D2 for ; Sat, 21 Jan 2023 03:29:46 -0800 (PST) Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by smtp-out2.suse.de (Postfix) with ESMTPS id 5140A5FFC8; Sat, 21 Jan 2023 11:29:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_rsa; t=1674300585; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=5syjoP68/X1yj4HDBfbMlhfi9N1S6g7T+QMIMt/oPX8=; b=gpWM2hDo+vCjQ4xw4JVKSPaz9Mz/4Iae9UEU795MN41r4KP8YTLTzHusMm/29LCLR1L36q qw4pikvS04wq3+FX82eSoJIeHsp9t5MgihNZvN9EjML2J3b3MmsNj2mtArlKWma6tBt2ok /+XutrD1lxd4sH256oSqRPJ6U1N6Ytc= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_ed25519; t=1674300585; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=5syjoP68/X1yj4HDBfbMlhfi9N1S6g7T+QMIMt/oPX8=; b=m5mnLxazxSC/EnFrtILhKcZfeR78ijOenbWBO58NVlGXSCbVjkW5uBwk3QH9AXrOL/unHj ZDzZHxULPeb1YiBA== Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by imap2.suse-dmz.suse.de (Postfix) with ESMTPS id D8F71138FE; Sat, 21 Jan 2023 11:29:44 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id KKH1M6jMy2O0EgAAMHmgww (envelope-from ); Sat, 21 Jan 2023 11:29:44 +0000 Message-ID: <86e68d3b-b029-5e82-5bbc-e0ccc2ae1d36@suse.cz> Date: Sat, 21 Jan 2023 12:29:44 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.6.1 Subject: Re: [PATCH mm-unstable] lib/Kconfig.debug: do not enable DEBUG_PREEMPT by default To: Hyeonggon Yoo <42.hyeyoo@gmail.com>, Andrew Morton , Christoph Lameter , Pekka Enberg , David Rientjes , Joonsoo Kim , Roman Gushchin Cc: Ingo Molnar , Johannes Weiner , Michal Hocko , Shakeel Butt , Muchun Song , Matthew Wilcox , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Peter Zijlstra , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Daniel Bristot de Oliveira , Valentin Schneider References: <20230121033942.350387-1-42.hyeyoo@gmail.com> Content-Language: en-US From: Vlastimil Babka In-Reply-To: <20230121033942.350387-1-42.hyeyoo@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 1/21/23 04:39, Hyeonggon Yoo wrote: > In workloads where this_cpu operations are frequently performed, > enabling DEBUG_PREEMPT may result in significant increase in > runtime overhead due to frequent invocation of > __this_cpu_preempt_check() function. > > This can be demonstrated through benchmarks such as hackbench where this > configuration results in a 10% reduction in performance, primarily due to > the added overhead within memcg charging path. > > Therefore, do not to enable DEBUG_PREEMPT by default and make users aware > of its potential impact on performance in some workloads. > > hackbench-process-sockets > debug_preempt no_debug_preempt > Amean 1 0.4743 ( 0.00%) 0.4295 * 9.45%* > Amean 4 1.4191 ( 0.00%) 1.2650 * 10.86%* > Amean 7 2.2677 ( 0.00%) 2.0094 * 11.39%* > Amean 12 3.6821 ( 0.00%) 3.2115 * 12.78%* > Amean 21 6.6752 ( 0.00%) 5.7956 * 13.18%* > Amean 30 9.6646 ( 0.00%) 8.5197 * 11.85%* > Amean 48 15.3363 ( 0.00%) 13.5559 * 11.61%* > Amean 79 24.8603 ( 0.00%) 22.0597 * 11.27%* > Amean 96 30.1240 ( 0.00%) 26.8073 * 11.01%* > > Signed-off-by: Hyeonggon Yoo <42.hyeyoo@gmail.com> Looks like it's there since the beginning of preempt and pre-git. But probably should be something for scheduler maintainers rather than mm/slab, even if the impact manifests there. You did Cc Ingo (the original author) so let me Cc the rest here. > --- > lib/Kconfig.debug | 5 ++++- > 1 file changed, 4 insertions(+), 1 deletion(-) > > diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug > index ddbfac2adf9c..f6f845a4b9ec 100644 > --- a/lib/Kconfig.debug > +++ b/lib/Kconfig.debug > @@ -1176,13 +1176,16 @@ config DEBUG_TIMEKEEPING > config DEBUG_PREEMPT > bool "Debug preemptible kernel" > depends on DEBUG_KERNEL && PREEMPTION && TRACE_IRQFLAGS_SUPPORT > - default y > help > If you say Y here then the kernel will use a debug variant of the > commonly used smp_processor_id() function and will print warnings > if kernel code uses it in a preemption-unsafe way. Also, the kernel > will detect preemption count underflows. > > + This option has potential to introduce high runtime overhead, > + depending on workload as it triggers debugging routines for each > + this_cpu operation. It should only be used for debugging purposes. > + > menu "Lock Debugging (spinlocks, mutexes, etc...)" > > config LOCK_DEBUGGING_SUPPORT