From owner-freebsd-current@FreeBSD.ORG Sun Jul 31 21:04:48 2005 Return-Path: X-Original-To: freebsd-current@freebsd.org Delivered-To: freebsd-current@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id 9517916A41F for ; Sun, 31 Jul 2005 21:04:48 +0000 (GMT) (envelope-from julian@elischer.org) Received: from postoffice.vicor-nb.com (postoffice.vicor.com [69.26.56.52]) by mx1.FreeBSD.org (Postfix) with ESMTP id 42D1D43D46 for ; Sun, 31 Jul 2005 21:04:48 +0000 (GMT) (envelope-from julian@elischer.org) Received: from localhost (localhost [127.0.0.1]) by postoffice.vicor-nb.com (Postfix) with ESMTP id 079054CE94A; Sun, 31 Jul 2005 14:04:48 -0700 (PDT) Received: from postoffice.vicor-nb.com ([127.0.0.1]) by localhost (postoffice.vicor-nb.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id 78347-02; Sun, 31 Jul 2005 14:04:47 -0700 (PDT) Received: from [208.206.78.97] (julian.vicor-nb.com [208.206.78.97]) by postoffice.vicor-nb.com (Postfix) with ESMTP id 558F14CE910; Sun, 31 Jul 2005 14:04:47 -0700 (PDT) Message-ID: <42ED3CEE.2090803@elischer.org> Date: Sun, 31 Jul 2005 14:04:46 -0700 From: Julian Elischer User-Agent: Mozilla/5.0 (X11; U; FreeBSD i386; en-US; rv:1.7.8) Gecko/20050629 X-Accept-Language: en, hu MIME-Version: 1.0 To: Julian Elischer References: <42ED3ADE.9040508@elischer.org> In-Reply-To: <42ED3ADE.9040508@elischer.org> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-Virus-Scanned: by amavisd-new at postoffice.vicor.com Cc: FreeBSD Current Subject: Re: 6.0: Unable to make disks 100% busy in file system reads. X-BeenThere: freebsd-current@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Discussions about the use of FreeBSD-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sun, 31 Jul 2005 21:04:48 -0000 Julian Elischer wrote: > On my 4.x systems, the following comand makes disks go about 100% > (well, 98%) busy > (measured by systat -vmstat). > > tar cf /dev/null /usr > > I know that some versions of tar recognise /dev/null as an output > device and > cheat, so to be sure I confirmed that > > tar cf - /usr | dd of=/dev/null bs=128k > > has the same result (IDE drive). > > The same command run on 6.0 has difficulty keeping the drives 70% busy. > (though for sume unknow reason I have seen it get to 87% for up to > 10 or 15 seconds at a time). > > measured by gstat AND systems -vmstat. > > cpu usage at the time: > > 21.0%Sys 2.3%Intr 0.5%User 0.0%Nice 76.2%Idl > 17.9%Sys 2.0%Intr 0.5%User 0.0%Nice 79.5%Idl > it is noticable that the times that the disk usage goes higher (e.g. 87%) > the system idle time is also higher, and sys time drops to about 6% so > I am presuming it is a set of large files being traversed at that time. > Softupdates is NOT enabled. > > Now if I start TWO of the work processses, the drive usage climbs to a > pretty permanent 98% which is quite acceptable. So, it's not geom, > at least, not in any direct manner. > > The interesting part is that 4.11 is able to force this disk usage > with just one > work process. > > it seems to be something to do with the speed of the return > information for the read > from disk.. Some scheduler interaction possibly, along with some side > effects of the > new. .. queueing behaviour. > I've been looking at the way that the scheduling works and not seen > anything that > really stands out.. If anyone has any ideas of other things to look at > I'm all ears.. for example.. is the sequential lookahead working as well in the new world... > > > Julian > > _______________________________________________ > freebsd-current@freebsd.org mailing list > http://lists.freebsd.org/mailman/listinfo/freebsd-current > To unsubscribe, send any mail to > "freebsd-current-unsubscribe@freebsd.org"