Date: Sat, 22 Sep 2001 00:00:04 -0700 From: Terry Lambert <tlambert2@mindspring.com> To: Luigi Rizzo <luigi@info.iet.unipi.it> Cc: Andrew Gallatin <gallatin@cs.duke.edu>, hackers@freebsd.org, wpaul@freebsd.org Subject: Re: any reason to use m_devget in the "dc" driver ? Message-ID: <3BAC36F4.1B9E8E2E@mindspring.com> References: <200109220558.HAA64949@info.iet.unipi.it>
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Luigi Rizzo wrote: > > I probably missed some emails ? > In any case i was only concerned about the additional copy > done by m_devget when the controller can already DMA into > an mbuf, and there are no alignment constraints. I guess we are talking about a protocol other than IP? The ethernet header is 14 bytes in length, which means that the elements in the IP header are not longword aligned, unless the card can DMA onto a 2 byte boundary, and does so, to ensure that the IP header starts on a 16 byte boundary, and therefore the contents are correctly aligned for direct reference in a single bus cycle (or at all, on Alpha, where unaligned access is not permitted). -- Terry To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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