Date: Thu, 12 Feb 2004 22:33:06 +0800 From: Dung Patrick <dkt@digitalme.com> To: gallatin@cs.duke.edu, Cc: freebsd-hackers@freebsd.org Subject: Re: Re: Zero copy sockets question Message-ID: <1076596386.c6c7c260dkt@digitalme.com>
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Correct me if I am wrong: To use the zero copy 'receive' on i386, you need to set the MTU to 4096 bytes(page size) or 4096 multiples. If it is true, until zero copy receive can do auto fitting, I think zero copy receive is more useful in gigabit ethernet than in fast ethernet (I assume MTU 1500(or smaller) is suitable for fast ethernet/Internet.) Patrick -----Original Message----- From: Andrew Gallatin <gallatin@cs.duke.edu> To: Dung Patrick <dkt@digitalme.com> Date: Thu, 12 Feb 2004 09:17:46 -0500 (EST) Subject: Re: Zero copy sockets question 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
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