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 1BsiOr-0005F9-Ur for user-mode-linux-devel@lists.sourceforge.net; Thu, 05 Aug 2004 06:35:17 -0700 Received: from zsc3s004.nortelnetworks.com ([47.81.138.65]) by sc8-sf-mx2.sourceforge.net with esmtp (Exim 4.34) id 1BsiOr-0002gi-KA for user-mode-linux-devel@lists.sourceforge.net; Thu, 05 Aug 2004 06:35:17 -0700 Message-ID: <41123785.5040004@nortelnetworks.com> From: Joe Marzot MIME-Version: 1.0 Subject: Re: [uml-devel] Q: UML thread communication - scheduling oddness References: <200408050020.i750Kwvv009127@ccure.user-mode-linux.org> Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit 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: Thu, 05 Aug 2004 09:35:01 -0400 To: Jeff Dike Cc: Joe Marzot , user-mode-linux-devel@lists.sourceforge.net, Randy Macleod That's an excellent theory esp. ince we do not see the problem typically on a host with more memory. I presume there are tricks we can play to get our memory not to be swapped out (recall a discussion on that here). Could you add a few sentences though on the delivery mechnisms for the the packets to the kernel thread and to userspace. I saw a poll() on the pollfds array which has the taps fd in it but this is a non-blocking poll and I could not trace to how often it is called and what triggers it - I also saw the sigio handler but I could not see who was generating the SIGIO - is that how the userspace thread is woken up? If there is some thing else I can read to get some background that would help...otherwise its back to the source of course. thank you kindly, Giovanni Jeff Dike wrote: > gmarzot@nortelnetworks.com said: > > That is, if I run a little busy loop > > /mnt/plankton/stress --cpu 1 --io 1 > > on the server side, the round trip time for messages is greatly > > *improved*. without this activity and a basically dormant server side > > UML the round trip times show considerable variabilty with gaps on the > > order of seconds. > > How's this for a theory: The server's host is short on memory. A UML > which > is answering pings every second or so can be considered pretty idle, and > thus > a good candidate to have its pages swapped out. So, this happens, and when > a ping comes in, UML needs to be swapped back in, causing your long and > unpredictable delays. > > Running a busy loop in the UML makes it busy from the point of view of the > host and prevents it from being swapped out, giving you nice ping > latencies. > > Jeff > > ------------------------------------------------------- This SF.Net email is sponsored by OSTG. Have you noticed the changes on Linux.com, ITManagersJournal and NewsForge in the past few weeks? Now, one more big change to announce. We are now OSTG- Open Source Technology Group. Come see the changes on the new OSTG site. www.ostg.com _______________________________________________ User-mode-linux-devel mailing list User-mode-linux-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/user-mode-linux-devel