Much improved sendfile(2) kernel implementation

[David Malone]

On Fri, Sep 22, 2006 at 11:48:23PM +0100, Robert Watson wrote:
> The impact of TSO is clearly dramatic, especially when combined with the 
> patch, but I'm a bit concerned by the drop in performance in the patched 
> non-TSO case.  For network cards which will always have TSO enabled, this 
> isn't an issue, but do we see a similar affect for drivers without TSO?  
> What can we put this drop down to?

We probably also need to make sure that any performance increase
in TSO isn't due to us getting TCP congestion control wrong. I think
in Linux they had problems when they first introduced TSO because
TCP was advancing the congestion window by a TSO-sized chunk instead
of a wire packet. OTOH, I think Andre and Drew's tests are low-latency,
so congestion control isn't likely to be playing a big role, so the
improvements are unlikely to be due to this.

	David.