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<font size=3>At 09:58 AM 12/18/2004, Hal Rosenstock wrote:<br>
<blockquote type=cite class=cite cite="">On Sat, 2004-12-18 at 12:55,
Roland Dreier wrote:<br>
> Surely link width and/or speed can't change without the port
state<br>
> changing, can they? As I understand it, the link layer
can't<br>
> renegotiate this sort of thing without bringing the link down.
In<br>
> which case ULPs only need to refresh their rate information when
they<br>
> get one of the existing port state change events.<br><br>
Yes, port state change is sufficient to take care of this.<br><br>
> (If the link rate can change without any notice, then static rate
for<br>
> RC is meaningless since a link could change from 4X to 1X
without<br>
> disturbing existing connections).</blockquote><br>
Keep in mind that unless one is monitoring all of the intermediate port
states, then this can change without it being noticed by the CA port if
does not change. Same would apply if a switch fabric were
reconfigured such that a LID took a new path through the fabric and the
rate was impacted by either link width change or signaling rate
change. Static rate needs to understand the entire end-to-end path
and whenever it is updated to be effective. For IP over IB using
UD, there are many paths which can be taken so it is not clear what would
be an appropriate IPD if one path the data rate is 500 MB/s and on
another it is 6GB/s. Should this be dominated by the lowest path
speed or should one pursue VL arbitration to segregate this type of
workload based on what the endnode believes is the proper QoS? IPD
does not really work for UD in the end and our intention with the
technology was to avoid trying to bandwidth manage UD other than through
VL / switch port arbitration policies.<br><br>
Mike </font></body>
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