Date: Mon, 8 Sep 2003 09:38:02 -0400 (EDT) From: Andrew Gallatin <gallatin@cs.duke.edu> To: Luigi Rizzo <rizzo@icir.org> Cc: freebsd-net@freebsd.org Subject: Re: TCP Segmentation Offload Message-ID: <16220.34362.594825.422966@grasshopper.cs.duke.edu> In-Reply-To: <20030906090701.A3163@xorpc.icir.org> References: <16216.63066.954104.582195@grasshopper.cs.duke.edu> <20030906090701.A3163@xorpc.icir.org>
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Luigi Rizzo writes: > On Fri, Sep 05, 2003 at 04:47:22PM -0400, Andrew Gallatin wrote: > > > > I've been reading a little about TCP Segmentation Offload (aka TSO). > > We don't appear to support it, but at least 2 of our supported nics > > (e1000 and bge) apparently could support it. > > i believe there is more commercial hype than actual savings in doing > TCP Segmentation Offload. > > With delayed acks (or better, "ack every second packet"), > the sender's TCP typically sends out two > packets at a time. Without delayed acks, it is just one at a > time. So yes, you avoid looping in tcp_output() twice, but I think that the loop in tcp_output() is not such a big deal. IMHO, the bigger savings is from not making extra trips through the driver, and from allowing the adapter to perform a smaller number of large DMAs. Naturally, this is all just speculation until there's an actual implementation which can be profiled ;) Drew
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