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Date: Wed, 9 Sep 2009 13:26:22 -0400 (EDT)
From: Christoph Lameter <cl@...ux-foundation.org>
To: Eric Dumazet <eric.dumazet@...il.com>
cc: netdev@...r.kernel.org
Subject: Re: UDP regression with packets rates < 10k per sec
On Wed, 9 Sep 2009, Eric Dumazet wrote:
> I have no idea how you run the test then, and how are computed time deltas.
>
> Are you clocks synchronized to less than one us ? How is it done ?
Packets are sent one way and include a timestamp. Once in a while (probe
interval) a packet is sent back to the sender (with the timestamp the
sender took earlier). The sender takes a second timestamp and
calculates the latency by dividing by two.
Seen this approach in multiple middleware test programs. Clocks are
typically not synchronized enough to actually compare timestamps from two
systems.
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