Date: Sun, 21 Jun 2009 17:46:14 +0200 From: =?utf-8?Q?Dag-Erling_Sm=C3=B8rgrav?= <des@des.no> To: Wojciech Puchar <wojtek@wojtek.tensor.gdynia.pl> Cc: freebsd-hackers@freebsd.org Subject: Re: is RTL8139 THAT bad? Message-ID: <86eitdy4hl.fsf@ds4.des.no> 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 %2B0200 (CEST)") References: <alpine.BSF.2.00.0906211709420.1184@wojtek.tensor.gdynia.pl>
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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
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