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 E7FB2CDB47E for ; Wed, 18 Oct 2023 07:57:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1344633AbjJRH5j (ORCPT ); Wed, 18 Oct 2023 03:57:39 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52934 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230140AbjJRH5g (ORCPT ); Wed, 18 Oct 2023 03:57:36 -0400 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 45FC5F7 for ; Wed, 18 Oct 2023 00:57:34 -0700 (PDT) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 488D0C433C8; Wed, 18 Oct 2023 07:57:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1697615853; bh=+Mrul8FDzJtGcrh5YRbVdL5kFqOw6AV3Rg2td373w+Y=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=QFRcoudqconpP0opYr9xXtP6vzoY39iQamDCn3d6bnWBWtlmuFXdqce2q1gLF8dtM get5IK5YgnASGZLf4njqA7VM60zoqm/kswtdlbSn+dNfUIY1v4nPFI/zsFrXUawTku SnjQ0rbEcyOoBFfix7psouWj+xTHyBDfYa3syZ6Y= Date: Wed, 18 Oct 2023 09:57:25 +0200 From: Greg Kroah-Hartman To: Oliver Sang Cc: Max Kellermann , oe-lkp@lists.linux.dev, lkp@intel.com, Linux Memory Management List , linux-kernel@vger.kernel.org, ying.huang@intel.com, feng.tang@intel.com, fengwei.yin@intel.com Subject: Re: [linux-next:master] [drivers/char/mem] 1b057bd800: stress-ng.splice.ops_per_sec -99.8% regression Message-ID: <2023101836-backtalk-mystified-d197@gregkh> References: <202310172247.b9959bd4-oliver.sang@intel.com> <2023101759-front-ember-6354@gregkh> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Oct 18, 2023 at 03:07:20PM +0800, Oliver Sang wrote: > hi, Greg Kroah-Hartman, > > On Tue, Oct 17, 2023 at 06:56:56PM +0200, Greg Kroah-Hartman wrote: > > On Tue, Oct 17, 2023 at 11:06:42PM +0800, kernel test robot wrote: > > > > > > > > > Hello, > > > > > > kernel test robot noticed a -99.8% regression of stress-ng.splice.ops_per_sec on: > > > > > > > > > commit: 1b057bd800c3ea0c926191d7950cd2365eddc9bb ("drivers/char/mem: implement splice() for /dev/zero, /dev/full") > > > https://git.kernel.org/cgit/linux/kernel/git/next/linux-next.git master > > > > > > testcase: stress-ng > > > test machine: 64 threads 2 sockets Intel(R) Xeon(R) Gold 6346 CPU @ 3.10GHz (Ice Lake) with 256G memory > > > parameters: > > > > > > nr_threads: 100% > > > testtime: 60s > > > class: pipe > > > test: splice > > > cpufreq_governor: performance > > > > > > > > > In addition to that, the commit also has significant impact on the following tests: > > > > > > +------------------+-------------------------------------------------------------------------------------------------+ > > > | testcase: change | stress-ng: stress-ng.splice.ops_per_sec 38.9% improvement | > > > > So everything now goes faster, right? -99.8% regression means 99.8% > > faster? > > let me clarify. > > our auto bisect captured this commit as 'first bad commit' in two tests. > > Test 1: > > it found a (very big) regression comparing to parent commit. > > 19e3e6cdfdc73400 1b057bd800c3ea0c926191d7950 > ---------------- --------------------------- > %stddev %change %stddev > \ | \ > 12433266 -99.8% 22893 ± 3% stress-ng.splice.ops_per_sec > > the detail data for parent in multi-runs: > "stress-ng.splice.ops_per_sec": [ stress-ng is a performance test? > 12444442.19, > 12599010.87, > 12416009.38, > 12494132.89, > 12286766.76, > 12359235.82 > ], > > for 1b057bd800: > "stress-ng.splice.ops_per_sec": [ > 24055.57, > 23235.46, > 22142.13, > 23782.13, > 21732.13, > 22415.46 > ], > > so this is much slower. That's odd given that as was pointed out, this test does not even touch the code paths that this patch changed. confused, greg k-h