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

On Thu, Oct 27, 2011 at 12:44:22PM -0400, Greg Troxel wrote:
> one has to wonder how bpf works when tso is enabled.  are the packets
> read back from the card, or are they also created in software and then
> discarded?

The mbuf passed to the adapter is also passed to bpf_mtap(),
so bpf_mtap() gets the tso packet and not the on-wire packets when
tso is in use.

AFAIK bpf_mtap() doesn't do any attempts at doing something special
with TSO mbufs it could get. So I guess tcpdump is getting the TSO
buffer ...

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

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