Subject: Re: TSO on wm(4) (Intel Pro/1000): i82546 vs i8254EI vs others?
To: None <>
From: YAMAMOTO Takashi <>
List: tech-net
Date: 05/24/2005 11:13:15

> For a send-only workload for ttcp, I expect TSO to roughly halve CPU
> overhead.  The 82544ei shows a meagre gain, on the order of lowering
> CPU use for a 123 Mbyte/sec send from 50% to 45%. (the gap may be
> narrower, I didn't measure the non-TSO case carefully). Thus, to me,
> with those expectaions, advertising TSO for an 82544 appears rather
> like false advertising.
> I'd be much happier if the driver printed a message warning when
> attaching an 82544, to the effect that TSO doesn't gain anything
> signficant due to a hardware errata.  Or print a short warning,
> and explain the issue in detail in the manpage. Or _something_.
> Advertising TSO, and then having it manifestly not work as expected,
> isn't going to make users happy.  Or at least, not this user.
- i don't think if_capabilities implies any perfomance gains.
  it just mean if it works or not.

- how much you gain from offloading depends on network stack implementation.
  do you want to re-evaluate each drivers/devices and flip capabilities,
  whenever network code is changed?  i don't think it's realistic.

in any case, if you want to discourage users to use the functionality,
manpage is a right place to change, IMO.