From owner-freebsd-current  Fri Jun  1 14:56: 1 2001
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Date: Fri, 01 Jun 2001 14:56:16 -0700
From: Terry Lambert <tlambert2@mindspring.com>
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To: Jonathan Lemon <jlemon@flugsvamp.com>
Cc: tlambert@primenet.com, current@freebsd.org
Subject: Re: PATCH: media option for ethernet hw checksum
References: <200105310028.f4V0Sbu77564@prism.flugsvamp.com>
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Jonathan Lemon wrote:
> >Here is a patch I have locally that would be useful for Bill Paul,
> >I think.  I know, we could use "flag0" for this, but it seems to
> >me that this will be an increasingly common option in hadware.
> >
> >I know Bill had to set this manually as a compile time flag, for
> >lack of an option (same for the JMB Intel Gigabit card driver).
> 
> Um, why?  It shouldn't be an option.  Either the card supports it
> and it's turned on, or it doesn't and it's turned off.  If anything,
> perhaps there should be a sysctl to enable/disable all hw checksums
> for those who want a more end-to-end solution.

I think you are behind in this thread.  The answer is in
several parts:

1)	For some Gigabit cards, the host can do it faster;
	for others, it can not.  If you can have a machine
	with several different cards in it, then it needs
	to be a per card option.  This was my initial reason,
	since I have a local system with both Tigon II and
	Tigon III cards in it.

2)	For some topologies, it makes sense to turn off the
	checksum checking entirely for local link destinations,
	since the checksum is not really useful, but it is not
	possible to negotiate it off on an end-to-end basis,
	but you might want to avoid the overhead to get much
	closer to wire speeds on a local intra-cluster
	network.

-- Terry

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