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Date: Thu, 12 Feb 2004 09:26:16 -0500 (EST)
To: Dung Patrick <dkt@digitalme.com>
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cc: freebsd-hackers@freebsd.org
Subject: Re: Zero copy sockets question
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Dung Patrick writes:
 > Hi
 > 
 > I have read http://people.freebsd.org/~ken/zero_copy/
 > 
 > To correctly use zero copy receive, it seems it need to set the MTU to:
 > have to be at least page sized, and be aligned on page boundaries.

Yes.

 > So is the default MTU for ethernet network card 1500 works?

No, you need to have an MTU of at least PAGE_SIZE + headers.
And a NIC which is smart enough to do the header splitting.
Currently, the Alteon Tigon2 is the only nic which fits the bill.
I keep meaning to implement header splitting in the Myricom Myrinet
firmware, and I keep not getting time for it..

Note that send-side zero-copy works on any NIC, and with a standard
MTU.


Drew