From owner-svn-src-head@FreeBSD.ORG Sat May 28 19:18:30 2011 Return-Path: Delivered-To: svn-src-head@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id C4FC0106564A; Sat, 28 May 2011 19:18:30 +0000 (UTC) (envelope-from pieter@degoeje.nl) Received: from mx.utwente.nl (mx2.utsp.utwente.nl [130.89.2.13]) by mx1.freebsd.org (Postfix) with ESMTP id 34FB68FC12; Sat, 28 May 2011 19:18:29 +0000 (UTC) Received: from nox.student.utwente.nl (nox.student.utwente.nl [130.89.165.91]) by mx.utwente.nl (8.12.10/SuSE Linux 0.7) with ESMTP id p4SJ3hP4003548; Sat, 28 May 2011 21:03:43 +0200 From: Pieter de Goeje To: svn-src-all@freebsd.org Date: Sat, 28 May 2011 21:03:42 +0200 User-Agent: KMail/1.9.10 References: <201105131848.p4DIm1j7079495@svn.freebsd.org> In-Reply-To: <201105131848.p4DIm1j7079495@svn.freebsd.org> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <201105282103.43370.pieter@degoeje.nl> X-UTwente-MailScanner-Information: Scanned by MailScanner. Contact icts.servicedesk@utwente.nl for more information. X-UTwente-MailScanner: Found to be clean X-UTwente-MailScanner-From: pieter@degoeje.nl X-Spam-Status: No Cc: svn-src-head@freebsd.org, Matthew D Fleming , src-committers@freebsd.org Subject: Re: svn commit: r221853 - in head/sys: dev/md dev/null sys vm X-BeenThere: svn-src-head@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: SVN commit messages for the src tree for head/-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sat, 28 May 2011 19:18:30 -0000 On Friday 13 May 2011 20:48:01 Matthew D Fleming wrote: > Author: mdf > Date: Fri May 13 18:48:00 2011 > New Revision: 221853 > URL: http://svn.freebsd.org/changeset/base/221853 > > Log: > Usa a globally visible region of zeros for both /dev/zero and the md > device. There are likely other kernel uses of "blob of zeros" than can > be converted. > > Reviewed by: alc > MFC after: 1 week > This change seems to reduce /dev/zero performance by 68% as measured by this command: dd if=/dev/zero of=/dev/null bs=64k count=100000. x dd-8-stable + dd-9-current +-------------------------------------------------------------------------+ |+ | |+ | |+ | |+ x x| |+ x x x| |A |MA_|| +-------------------------------------------------------------------------+ N Min Max Median Avg Stddev x 5 1.2573578e+10 1.3156063e+10 1.2827355e+10 1.290079e+10 2.4951207e+08 + 5 4.1271391e+09 4.1453925e+09 4.1295157e+09 4.1328097e+09 7487363.6 Difference at 95.0% confidence -8.76798e+09 +/- 2.57431e+08 -67.9647% +/- 1.99547% (Student's t, pooled s = 1.76511e+08) This particular measurement was against 8-stable but the results are the same for -current just before this commit. Basically througput drops from ~13GB/sec to 4GB/sec. Hardware is a Phenom II X4 945 with 8GB of 800Mhz DDR2 memory. FreeBSD/amd64 is installed. This processor has 6MB of L3 cache. To me it looks like it's not able to cache the zeroes anymore. Is this intentional? I tried to change ZERO_REGION_SIZE back to 64K but that didn't help. Regards, Pieter de Goeje