On Fri, 27 Sep 2013, Scheffenegger, Richard wrote:
Hi Mikael,
the papers around DCTCP have probably the information you are looking
for (map/reduce type workloads, leading to incast issues - momentary
filling of queues; loosing the final segments of a TCP session [1],
which is likely with drop tail queue management policy, is well known to
result in timely retransmission timeout-type recoveries. Tweaking OS
time granularities down to recover in few milliseconds on paths that
usually have a few dozen microseconds delay is often not good enough,
but even that is not for cautious.
Ok, so this makes sense within a data center with ECN, but I fail to see
any substantial upside deploying this in an environment where RTT is in
the tens of ms because TCP won't have time to react.
I seem to remember reading about enhancement to TCP where packets are
actually sent out with spacing between packets instead of in line-rate
bursts. If everybody started doing that then I would imagine there would
be less tail-drop in large RTT environments with large TCP windows?
--
Mikael Abrahamsson email: swm...@swm.pp.se
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