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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: X-Rspamd-Queue-Id: 74A1CA0019 X-Rspam-User: X-Stat-Signature: e1nzhep7uao1ryp85g3ys373fk64ihgt X-Rspamd-Server: rspam01 X-HE-Tag: 1697615859-254266 X-HE-Meta: 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 cTC9FlLE XyQfTI2rzmLXiKq/vdostNKtae9+2sI7zZQC31G6lClULNy209AZQcFFa9X8Z99A6Yf3hQIRieMqgFgUf7FlxPkquOzfJeLb9AQkMgdsLPNrdeN6+vy+I1I1gM6yqsJ8h0AkwA7pzUr8oR5qOsrsH57IuRfPTlOtCzyb57eQYJX4SIP+6t80H8PMDa/Mw5hC1IbSHZKA6QK+Q4MKl0sCyyFiTlSqOIXhcMtqd95Y6BcgIuPrHd5fRN9gQbPTvaevMqFrJ1M5BRxIMXdqzZRFXB+h2V6xEJ0y0wreUNOq/hzOh9yfY5k5zjTaPcUVQR0D4q1z0 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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