Re: Re: Zero copy sockets question

From: Andrew Gallatin (gallatin_at_cs.duke.edu)
Date: 02/12/04

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    Date: Thu, 12 Feb 2004 10:29:24 -0500 (EST)
To: Dung Patrick <dkt@digitalme.com>

    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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