From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from sc8-sf-mx2-b.sourceforge.net ([10.3.1.12] helo=sc8-sf-mx2.sourceforge.net) by sc8-sf-list1.sourceforge.net with esmtp (Exim 4.30) id 1BC0is-0005f1-Dn for user-mode-linux-devel@lists.sourceforge.net; Fri, 09 Apr 2004 11:27:26 -0700 Received: from mail.gmx.net ([213.165.64.20]) by sc8-sf-mx2.sourceforge.net with smtp (Exim 4.30) id 1BC0ir-0007YW-OT for user-mode-linux-devel@lists.sourceforge.net; Fri, 09 Apr 2004 11:27:25 -0700 Message-ID: <195901c41e61$3132cb90$2000000a@schlepptopp> From: "roland" References: <185d01c41e23$5996cc00$2000000a@schlepptopp> <189201c41e30$d434cc70$2000000a@schlepptopp> <200404091626.i39GQqsf002414@ccure.user-mode-linux.org> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Subject: [uml-devel] uml responsivenes or "AS vs DEADLINE Scheduler on uml-host" - was: [uml-user] Network lags Sender: user-mode-linux-devel-admin@lists.sourceforge.net Errors-To: user-mode-linux-devel-admin@lists.sourceforge.net List-Unsubscribe: , List-Id: The user-mode Linux development list List-Post: List-Help: List-Subscribe: , List-Archive: Date: Fri, 9 Apr 2004 20:33:39 +0200 To: Jeff Dike Cc: Joern Bredereck , user-mode-linux-user@lists.sourceforge.net, user-mode-linux-devel@lists.sourceforge.net, mingo@elte.hu Hi ! I think i found an interesting "scheduling issue" which led me to switch the subject of the thread. joern reported network lags, i have seen some other mails reporting about this issue, i had experienced such lags myself and i remember reading mails, that the first pings after "upping" the network interfaces in uml tend to give slow response time. just for the fun, i switched to deadline i/o scheduler on the host (kernel param "elevator=deadline") and, after a first try, things seem to behave better with that scheduler! i generated the same i/o load on the host, hogged the cpu like hell, loadavg was >40) and i NEVER recognized the network-lags again. i also cpu- and i/o-hogged the uml itself, which resulted in big increase of the ping-times (from average 0.2ms to 600ms), but i NEVER saw that strange behaviour of uml responsiveness again (ping times >90s,"sendmsg: no buffer space available") , as when i did use the standard AS (Anticipatory) Scheduler. there where _some_ pings >2000ms, too - but this didn`t happen often and not so seriously as with "AS" & an "idle uml" - the uml seems to be more responsive in general when using deadline scheduler. I cannot tell, if there is a bug in AS or this is a "uml<->AS issue" which causes uml network lags, but at least there should be done some more testing to confirm, what i found. so, i would like to encourage other people doing some more tests - especially those, who experience network-lags! regards roland ps: funny: i have solved my "problem" by switching to a different scheduler - joern has (probably) solved it by switching to a later uml-release. so is it a scheduler or a uml issue ? or both? pps: >This causes UML to get swapped out because it's not doing anything > except answering a ping once in a while. mhhh - as far as i remember i didn`t see(vmstat) a single byte of uml or any other process being swapped out when running my test. general question: does heavy usage of buffers lead to processes being swapped out? ----- Original Message ----- From: "Jeff Dike" To: "roland" Cc: "Joern Bredereck" ; ; ; Sent: Friday, April 09, 2004 6:26 PM Subject: Re: [uml-user] Network lags > for_spam@gmx.de said: > > at least, i would be interested in getting to know: > > - why this happens > > - how to "tune" this, that it doesn`t happen > > - if this is expected behavour on "heavy loaded systems" or probably a uml > > or host-kernel bug > > As you said, you're making life hard for the host. > > My guess as to what's happening is this. > > You're generating a ton of IO which is pulling the host's memory into page > cache. This causes UML to get swapped out because it's not doing anything > except answering a ping once in a while. When it does have to answer a ping, > it needs to be swapped back in, which might be hard since you're sucking down > a lot of IO bandwidth. > > So, I don't think this says too much about whether anything's wrong with > either the host or UML. > > Once thing you might try is do the same IO with O_DIRECT. That won't pollute > the page cache. > > Jeff > ------------------------------------------------------- This SF.Net email is sponsored by: IBM Linux Tutorials Free Linux tutorial presented by Daniel Robbins, President and CEO of GenToo technologies. Learn everything from fundamentals to system administration.http://ads.osdn.com/?ad_id=1470&alloc_id=3638&op=click _______________________________________________ User-mode-linux-devel mailing list User-mode-linux-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/user-mode-linux-devel