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Date: Mon, 3 Feb 2003 16:18:41 -0500
Message-Id: <200302032118.h13LIfqN006832@buggy.badula.org>
From: Ion Badulescu <ionut@badula.org>
To: "Joakim Tjernlund" <Joakim.Tjernlund@lumentis.se>
Cc: "Jeff Garzik" <jgarzik@pobox.com>, <linux-kernel@vger.kernel.org>
Subject: Re: NETIF_F_SG question
In-Reply-To: <001501c2ca5b$f4b45990$020120b0@jockeXP>
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On Sun, 2 Feb 2003 02:39:41 +0100, Joakim Tjernlund <Joakim.Tjernlund@lumentis.se> wrote:
> 
> I think HW checksumming and SG are independent. Either one of them should
> not require the other one in any context.

They should be independent in general, but they aren't when the particular
case of TCP/IPv4 is concerned.

> Zero copy sendfile() does not require HW checksum to do zero copy, right?

Wrong...

> If HW checksum is present, then you get some extra performance as a bonus.

You get zerocopy, yes. :-) No HW cksum, no zerocopy.

Don't let this stop you, however. It's always possible that other networking
stacks will eventually make use of SG while not requiring HW TCP/UDP cksums.
None of them do right now, but...

> (hmm, one could make SG mandatory and the devices that don't support it can 
> implement it in their driver. Just an idea)

Not really, that way lies driver madness. The less complexity in the driver,
the better.

Ion
[starfire driver maintainer]

-- 
  It is better to keep your mouth shut and be thought a fool,
            than to open it and remove all doubt.
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