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Re: NetBSD 5.1 TCP performance issue (lots of ACK)

On Mon, Oct 24, 2011 at 06:26:19PM +0100, David Laight wrote:
> I've seen Linux stacks defer sending an ACK until the next? kernel
> clock tick. This will reduce the ACK count somewhat.
> In my case is caused problems with 'slow start' at the other end
> (which was also Linux).

In this case NetBSD sends nearly one ACK for every data packet received.
I suspect this is what is causing the performances issues.
Without deffering too much we can probably be clever here.

I also suspect it's a bug somewere, because in other condition NetBSD
doesn't send that much ACK. It seems that glusterfs is using
SO_SNDBUF/SO_RCVBUF, I wonder if this is what is causing this behavior.
Both are set to 512KB.

Manuel Bouyer <>
     NetBSD: 26 ans d'experience feront toujours la difference

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