Re: [ofa-general] Re: [PATCH RFC] RDMA/CMA: Allocate PS_TCPportsfrom the host TCP port space.

[David Miller <davem@davemloft.net>]

From: Andi Kleen <andi@firstfloor.org>
Date: 20 Aug 2007 01:27:35 +0200

> "Felix Marti" <felix@chelsio.com> writes:
> 
> > what benefits does the TSO infrastructure give the
> > non-TSO capable devices?
> 
> It improves performance on software queueing devices between guests
> and hypervisors. This is a more and more important application these
> days.  Even when the system running the Hypervisor has a non TSO
> capable device in the end it'll still save CPU cycles this way. Right now
> virtualized IO tends to much more CPU intensive than direct IO so any
> help it can get is beneficial.
> 
> It also makes loopback faster, although given that's probably not that
> useful.
> 
> And a lot of the "TSO infrastructure" was needed for zero copy TX anyways,
> which benefits most reasonable modern NICs (anything with hardware 
> checksumming)

And also, you can enable TSO generation for a non-TSO-hw device and
get all of the segmentation overhead reduction gains which works out
as a pure win as long as the device can at a minimum do checksumming.