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From: =?utf-8?Q?Dag-Erling_Sm=C3=B8rgrav?= <des@des.no>
To: Wojciech Puchar <wojtek@wojtek.tensor.gdynia.pl>
References: <alpine.BSF.2.00.0906211709420.1184@wojtek.tensor.gdynia.pl>
Date: Sun, 21 Jun 2009 17:46:14 +0200
In-Reply-To: <alpine.BSF.2.00.0906211709420.1184@wojtek.tensor.gdynia.pl>
	(Wojciech Puchar's message of "Sun, 21 Jun 2009 17:14:29 +0200
	(CEST)")
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Cc: freebsd-hackers@freebsd.org
Subject: Re: is RTL8139 THAT bad?
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Wojciech Puchar <wojtek@wojtek.tensor.gdynia.pl> writes:
> Why it's THAT bad?

http://svn.freebsd.org/base/head/sys/pci/if_rl.c

Scroll down past the copyright, license and attribution.  Read the
38-line comment that explains just how crappy this chip really is.

Executive summary: every single transmitted frame must be copied from
the mbuf into a DMA transmit buffer, and every single received frame
must be copied from the (quite small) DMA receive buffer into an mbuf.
In addition, the transmit queue can only hold four frames.

Other chips use scatter-gather lists and other mechanisms which allow
them to DMA frames straight out of or into mbufs.

DES
--=20
Dag-Erling Sm=C3=B8rgrav - des@des.no