>Slow start is such a critical thing to avoid internet meltdown, and with Linux
>becoming more and more popular we really cannot risk any experiments in release
>kernels here.
Agreed.
>The problem is at the sender: it doesn't send enough acks. Linux 2.2
I think the problem is the _receiver_ that is not sending the ack until
the ato expired if the sender is in slow-start for example. I think this
happens because we don't force an ack at the second frame received as
rfc1122 seems to state. As side effect we are also not opening fast enough
the cwnd on the sender side.
I think that this is the reason that MPI people got boosted by disabling
completly delayed acks (no need to wait ato to timeout anymore and cwnd
increase at an higer rate). Now I think that if delayed acks would work
right they woldn't need to disable them to get performances.
I had not yet feedback about my last patch (the one I sent yesterday with
the line of credits), to know if such patch works well as disabling
delacks completly while using MPI though, so I am not sure yet if my
theory has something to do with reality :-).
Andrea Arcangeli
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