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 B4003C27C76 for ; Thu, 26 Jan 2023 02:02:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230244AbjAZCCZ (ORCPT ); Wed, 25 Jan 2023 21:02:25 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53128 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229481AbjAZCCY (ORCPT ); Wed, 25 Jan 2023 21:02:24 -0500 Received: from out2.migadu.com (out2.migadu.com [188.165.223.204]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8BE5F5EF94 for ; Wed, 25 Jan 2023 18:02:23 -0800 (PST) Date: Wed, 25 Jan 2023 18:02:04 -0800 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1674698541; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=dP/00qm2xtIoOgxZ59rfAfeMc8lp52RZ82HChbdOra0=; b=URqM1W+zW3QAvh/0+OOEBnQl0aaQomsbz+tP9Q7hKsSBR1wJF0vbHtv9GWiWTzGBNPI/uI WJ/BHaI8tQ5gmHapNRBpgAC3ZakEA3pvi7+APpcy14mQCwPE+u78V2hlhXcUwqEGqnjsgJ X/M4KpCwZxGGxcTY8dzsJKgVCJssG/w= X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Roman Gushchin To: Hyeonggon Yoo <42.hyeyoo@gmail.com> Cc: Andrew Morton , Christoph Lameter , Pekka Enberg , David Rientjes , Joonsoo Kim , Vlastimil Babka , Ingo Molnar , Johannes Weiner , Michal Hocko , Shakeel Butt , Muchun Song , Matthew Wilcox , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH mm-unstable] lib/Kconfig.debug: do not enable DEBUG_PREEMPT by default Message-ID: References: <20230121033942.350387-1-42.hyeyoo@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230121033942.350387-1-42.hyeyoo@gmail.com> X-Migadu-Flow: FLOW_OUT Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Jan 21, 2023 at 12:39:42PM +0900, 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> Nice! I checkout my very simple kmem performance test (1M allocations 8-bytes allocations) and it shows ~30% difference: 112319 us with vs 80836 us without. Probably not that big for real workloads, but still nice to have. Acked-by: Roman Gushchin Thank you!