Re: issue with new TCP TSO stuff

[Andi Kleen <ak@muc.de>]

"David S. Miller" <davem@davemloft.net> writes:
>
> This shows up in testing where the connection is application limited.
> For example, an "scp" goes more slowly over TSO now, there are less
> cpu cycles available for the encryption.
>
> It's tricky to come up with a scheme to fix this.  I would love to be
> able to not do the page grabs/releases in the actual TSO frame.  I
> really haven't come up with a clean way to do that however.

Are you sure a few atomic_inc/dec are really causing noticeable
slowdown? That would surprise me unless you have lots of cache line
bouncing on a MP system.

What CPU did you test it on? Does it happen with only a single CPU?
And did you actually see them in some profile?

Assuming the struct page is in cache the P4 core is the slowest at
that that I know, but even on that one it should be in the noise on
the other overhead of talking to a NIC on a PCI bus.

Perhaps it is something else..

-Andi