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 byt= es(page size) or 4096 multiples. If it is true, until zero copy receive can do auto fitting, I think zero co= py receive is more useful in gigabit ethernet than in fast ethernet (I as= sume 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 >=20 > I have read http://people.freebsd.org/~ken/zero_copy/ >=20 > 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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