Subject: Re: bad TSO performance in 2.6.9-rc2-BK

From: Nivedita Singhvi <[email-masked]>
Date: Wed, 22 Sep 2004 13:56:17 -0700

David S. Miller wrote:

> The former rarely goes faster with TSO enabled simply
> because there is sufficient cpu and bus bandwidth to
> keep the card full.

At about 700MHz (ok, old, I know) or thereabouts, it
usually took > 1 CPU to drive a gigabit card, iirc,
about 1.5 CPUs or so.

> Whereas with something like SpecWEB the extra cpu and
> bus cycles are needed by other resources of the benchmark
> and thus performance goes up.

Yep..

> I have no idea why people think TSO will make some single
> stream TCP test go faster, it doesn't buy you more bytes
> on the wire :-)

True, if the card was already doing line speed,
no, as you say, it won't help making the stack go
faster :). If not, though, the gain in doing only
one pass down the stack, one route look up, etc in
place of multiple handoffs should help, correct?

thanks,
Nivedita