From: Jeff Dike <jdike@addtoit.com>
To: Joe Marzot <gmarzot@nortelnetworks.com>
Cc: user-mode-linux-devel@lists.sourceforge.net,
Randy Macleod <macleodr@nortelnetworks.com>
Subject: Re: [uml-devel] Q: UML thread communication - scheduling oddness
Date: Wed, 04 Aug 2004 20:20:58 -0400 [thread overview]
Message-ID: <200408050020.i750Kwvv009127@ccure.user-mode-linux.org> (raw)
In-Reply-To: Your message of "Wed, 04 Aug 2004 16:10:28 EDT." <411142B4.7000603@nortelnetworks.com>
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
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next prev parent reply other threads:[~2004-08-04 23:21 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-08-04 20:10 [uml-devel] Q: UML thread communication - scheduling oddness Joe Marzot
2004-08-05 0:20 ` Jeff Dike [this message]
2004-08-05 13:31 ` Michael Richardson
2004-08-05 13:35 ` Joe Marzot
2004-08-05 17:23 ` Jeff Dike
2004-08-05 16:45 ` Joe Marzot
2004-08-05 19:17 ` Jeff Dike
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