From owner-freebsd-performance@FreeBSD.ORG Wed Mar 22 17:53:41 2006 Return-Path: X-Original-To: freebsd-performance@freebsd.org Delivered-To: freebsd-performance@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id 02FB816A424 for ; Wed, 22 Mar 2006 17:53:41 +0000 (UTC) (envelope-from arne_woerner@yahoo.com) Received: from web30309.mail.mud.yahoo.com (web30309.mail.mud.yahoo.com [68.142.200.102]) by mx1.FreeBSD.org (Postfix) with SMTP id 6A14843D55 for ; Wed, 22 Mar 2006 17:53:37 +0000 (GMT) (envelope-from arne_woerner@yahoo.com) Received: (qmail 59010 invoked by uid 60001); 22 Mar 2006 17:53:36 -0000 DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=s1024; d=yahoo.com; h=Message-ID:Received:Date:From:Subject:To:Cc:In-Reply-To:MIME-Version:Content-Type:Content-Transfer-Encoding; b=mHKGYrYKuqG8RWpP4cS8a9yI/gz36PQITnyRw3K1Bp5JlZOHsDCYJG9THL/qaGymorEwYex76GN0DtJSXIL1CcfrJSCNPDfLuIkPB/HKdnkdTFtz0PqtOmgImGJ5woJq9KSEe3G+YCXBMKZULRffvkJyaN8AEA2pNENgFgbhJ7Q= ; Message-ID: <20060322175336.59008.qmail@web30309.mail.mud.yahoo.com> Received: from [213.54.73.238] by web30309.mail.mud.yahoo.com via HTTP; Wed, 22 Mar 2006 09:53:36 PST Date: Wed, 22 Mar 2006 09:53:36 -0800 (PST) From: Arne Woerner To: "Jin Guojun \[VFFS\]" In-Reply-To: <442187FE.3060300@lbl.gov> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: 8bit Cc: freebsd-performance@freebsd.org, Gary Thorpe , oxy@field.hu Subject: Re: packet drop with intel gigabit / marwell gigabit X-BeenThere: freebsd-performance@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Performance/tuning List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 22 Mar 2006 17:53:41 -0000 --- "Jin Guojun [VFFS]" wrote: >Arne Woerner wrote: >> What did we show by this <
> test? I thoughtthat >> would prove the memory bandwidth is about 8Gbit/sec(1GByte/sec; >> 2 * >number>/2^30). >> > It depends on how you use /dev/zero. > dd of=/dev/null if=/dev/zero bs=4k count=100k > tests cache speed % dd of=/dev/null if=/dev/zero bs=4k count=100k 102400+0 records in 102400+0 records out 419430400 bytes transferred in 0.204511 secs (2050894814 bytes/sec) about 32Gbit/sec? > dd of=/dev/null if=/dev/zero bs=4m count=100 > tests memory bandwidth if your cache is less than 2 MB > % dd of=/dev/null if=/dev/zero bs=4m count=100 100+0 records in 100+0 records out 419430400 bytes transferred in 2.587341 secs (162108677 bytes/sec) about 2.4Gbit/sec? I had an mpeg encoder in the background, when i did those benchmarks... :-) > Now you may give me the real memory bandwidth on your > system :-) > I would expect something around 500. > Hmm... 500Mbit/sec? even if i divide 2.4Gbit by 4, i still get 600Mbit/sec on a quite busy (50%) system... Oh... The docu TV series episode is over now and I re-ran the tests: % dd of=/dev/null if=/dev/zero bs=4m count=100 100+0 records in 100+0 records out 419430400 bytes transferred in 1.513610 secs (277106012 bytes/sec) % dd of=/dev/null if=/dev/zero bs=4k count=500k 512000+0 records in 512000+0 records out 2097152000 bytes transferred in 0.945430 secs (2218199591 bytes/sec) > Notice that your memory copy speed will be one half of it. > Why "half"? dd causes two copies but counts each byte just once... Maybe "dd" in combination with /dev/zero is not the right way to measure memory bandwidth? -Arne __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com