Date: Thu, 12 Feb 2004 10:29:24 -0500 (EST) From: Andrew Gallatin <gallatin@cs.duke.edu> To: Dung Patrick <dkt@digitalme.com> Cc: freebsd-hackers@freebsd.org Subject: Re: Re: Zero copy sockets question Message-ID: <16427.39892.876236.150143@grasshopper.cs.duke.edu> In-Reply-To: <1076596386.c6c7c260dkt@digitalme.com> References: <1076596386.c6c7c260dkt@digitalme.com>
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Dung Patrick writes: > 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. No, just larger than a page-size plus headers. FreeBSD's tcp automagically sets the mss to a page-sized multiple for large MTUs. And you need a nic which can do header splitting (ie, DMA the headers and the payload to different places in the host). > 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.) Fast ethernet is slow enough, it doesn't really make sense there. These days, one could argue that it really only makes sense for 10GbE. Drew
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