[OpenAFS] tcpoob timeline

Jeffrey Altman jaltman@secure-endpoints.com
Fri, 26 Oct 2012 21:00:59 -0400

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On 10/26/2012 6:40 PM, Jeffrey Altman wrote:
> The argument in favor of a TCP based solution is that RX cannot go fast=

> enough.  Andrew's claim is that RX cannot use a window size greater tha=
> 43.75K because of the 32 packet window limitation in 1.6.  The fact is
> that this limitation is not a protocol limitation but an implementation=

> limitation.  Andrew points to Simon Wilkinson's past talks on RX as a
> justification for this restriction.  Of course, Simon's talks also
> provide the road map for how to remove the bottlenecks and permit the
> full window size of 256 packets to be used without performance
> degradation.  When combined with Jumbograms a window can support up to
> 2MB of application data per call without any changes to the protocol.

A correction here.  The maximum window size is 358KB with the existing
limit of 1440 bytes per packet since the existing jumbo gram
implementation combines multiple RX packets into a single transmission
unit but does not increase the number of packets in the window.
However, it is possible to implement a packet size negotiation in RX
which would permit the maximum packet size to be increased to just under
64K.  64K packets combined with the current 256 packet window size can
permit saturation of a 10Gbit pipe with a single RX call.

Jeffrey Altman

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