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Wed, 15 Jun 2022 12:36:40 +0000 Date: Wed, 15 Jun 2022 13:36:40 +0100 From: Matthew Wilcox To: Yin Fengwei Cc: kernel test robot , LKML , lkp@lists.01.org, lkp@intel.com, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org Subject: Re: [LKP] Re: [mm/readahead] 793917d997: fio.read_iops -18.8% regression Message-ID: References: <20220418144234.GD25584@xsang-OptiPlex-9020> <1e8deaea-5a05-1846-d51c-b834beb9f23e@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <1e8deaea-5a05-1846-d51c-b834beb9f23e@intel.com> ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1655296614; a=rsa-sha256; cv=none; b=Um1F5npCs0UfsSGh0g29xiWET3srdMS79XhjnRaA0qM8PPsStmfBjOuFIEbdQV3+8P2UjC vukOyLPyREbNg5XYSFdG1VWmI9QRbt/DUyPCZf4mbEtr++NZccFMQChU5Kap2INfeiLw1L D4ujfCyA0J6VQY3468S/yczyVuDbc9I= ARC-Authentication-Results: i=1; imf19.hostedemail.com; dkim=pass header.d=infradead.org header.s=casper.20170209 header.b=vWlkI0pg; dmarc=none; spf=none (imf19.hostedemail.com: domain of willy@infradead.org has no SPF policy when checking 90.155.50.34) smtp.mailfrom=willy@infradead.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1655296614; h=from:from:sender:reply-to:subject:subject: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:dkim-signature; bh=5lqEWJkgj4WjPMuFW/4um7Uq+N/W4NBmyjYBaPvODgA=; b=pZ75V1R81RW+aBE4NwmRyX1ZdEASnYyhM1ilBoAkBnnR3yFjy6eJIxzf8Q+jsKMRJsieA0 qQIeoEAcAf1PhcB8iYKiAzgo/Qbl4WYYDH8ZgvUXquKzBVTgcCESzdzTfOU8uL90kQGCvj 4BY3WbGlwq67mOXQAcJilb+1vn3mL/0= Authentication-Results: imf19.hostedemail.com; dkim=pass header.d=infradead.org header.s=casper.20170209 header.b=vWlkI0pg; dmarc=none; spf=none (imf19.hostedemail.com: domain of willy@infradead.org has no SPF policy when checking 90.155.50.34) smtp.mailfrom=willy@infradead.org X-Rspam-User: X-Stat-Signature: nb3rt5u5fpxts51ertnbkhe7y5yjoeen X-Rspamd-Queue-Id: 831721A0082 X-Rspamd-Server: rspam08 X-HE-Tag: 1655296614-340041 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, Jun 15, 2022 at 02:38:24PM +0800, Yin Fengwei wrote: > On 4/19/2022 1:08 AM, Matthew Wilcox wrote: > > > > I'm on holiday today, but adding linux-fsdevel and linux-mm so relevant > > people know about this. > > > > Don't focus on the 18% regression, focus on the 240% improvement on the > > other benchmark ;-) > > > > Seriously, someone (probably me) needs to dig into what the benchmark > > is doing and understand whether there's a way to avoid (or decide this > > regression isn't relevant) while keeping the performance gains elsewhere. > With: > commit b9ff43dd27434dbd850b908e2e0e1f6e794efd9b > Author: Matthew Wilcox (Oracle) > Date: Wed Apr 27 17:01:28 2022 -0400 > > mm/readahead: Fix readahead with large folios > > the regression is almost gone: That makes sense. I did think at the time that this was probably the cause of the problem. > commit: > 18788cfa236967741b83db1035ab24539e2a21bb > b9ff43dd27434dbd850b908e2e0e1f6e794efd9b > > 18788cfa23696774 b9ff43dd27434dbd850b908e2e0 > ---------------- --------------------------- > fail:runs %reproduction fail:runs > | | | > 4698:9 -36360% 1426:3 dmesg.timestamp:last > 3027:9 -22105% 1037:3 kmsg.timestamp:last > %stddev %change %stddev > \ | \ > 0.39 ±253% -0.3 0.09 ±104% fio.latency_1000us% > 0.00 ±141% +0.0 0.01 fio.latency_100ms% > 56.60 ± 5% +10.3 66.92 ± 8% fio.latency_10ms% > 15.65 ± 22% -1.3 14.39 ± 17% fio.latency_20ms% > 1.46 ±106% -0.5 0.95 ± 72% fio.latency_2ms% > 25.81 ± 25% -9.2 16.59 ± 18% fio.latency_4ms% > 0.09 ± 44% +0.9 1.04 ± 22% fio.latency_50ms% > 0.00 ±282% +0.0 0.02 ±141% fio.latency_750us% > 13422 ± 6% -1.4% 13233 fio.read_bw_MBps <----- A stddev of 6% and a decline of 1.4%? How many tests did you run to make sure that this is a real decline and not fluctuation of one-quarter-of-one-standard-devisation?