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[Xen-devel] Re: Network buffering of remus

To: Frank Pan <frankpzh@xxxxxxxxx>
Subject: [Xen-devel] Re: Network buffering of remus
From: Brendan Cully <brendan@xxxxxxxxx>
Date: Mon, 23 Aug 2010 09:39:29 -0700
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On Monday, 23 August 2010 at 13:40, Frank Pan wrote:
> Hi,
> I'm doing researches on remus and have a question about its network buffering.
> I use the code in the xen unstable tree.
> I've run a guest and remus with network buffering(without --no-net),
> using the default interval 200ms. Then I ping the guest on the 3rd
> machine(other than primary and backup).
> I found that the average delay is about 30~50 ms, but I think it
> should be larger than 100ms.(due to network buffering, the output
> packet could be held for 0~200ms)
> Did I make anything wrong with the idea of network buffering? Or did I
> make any mistake during the test?

You'll probably want to test with something a bit more systematic than
ping. If ping sends a packet to the protected machine just before the
end of an epoch, the response won't be buffered very long at all. On
the other hand, if ping sends its packet at the start of an epoch, the
response will be delayed for the entire epoch length. By default, ping
sends packets infrequently, and the delay between pings isn't
particularly rigid, so you'll get jumpy results with it.

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