Date: Tue, 29 May 2001 23:52:15 -0500 From: Bob Willcox <bob@immure.com> To: Giorgos Keramidas <keramidi@otenet.gr> Cc: Jesper Skriver <jesper@skriver.dk>, hackers list <freebsd-hackers@FreeBSD.ORG> Subject: Re: How to disable software TCP checksumming? Message-ID: <20010529235215.A60177@luke.immure.com> In-Reply-To: <20010530045200.A1031@hades.hell.gr>; from keramidi@otenet.gr on Wed, May 30, 2001 at 04:52:00AM %2B0300 References: <20010529144114.I19771@luke.immure.com> <20010529221107.C49875@skriver.dk> <20010529155212.M19771@luke.immure.com> <20010530045200.A1031@hades.hell.gr>
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On Wed, May 30, 2001 at 04:52:00AM +0300, Giorgos Keramidas wrote: > On Tue, May 29, 2001 at 03:52:12PM -0500, Bob Willcox wrote: > | > | and may prevent the upper layers from checking the CRC on input. > > There are good reasons why checksumming in upper layers should not be disabled > even if some lower layer does checksumming of its own. I recall reading some > good points on this one at "TCP/IP Illustrated, Volume I" from (now late) > Richard W. Stevens. > > In fact, this is exactly what the sysctl knob net.inet.udp.checksum is there > for. The knob having a default value of 1 (checksumming enabled), means that > checksumming is used. > > If you do change checksumming in TCP, please provide a similar knob for that > protocol, and have it set to a default of 1 (still enabled). This way if > someone feels comfortable to have checksums disabled in TCP, or some higher > layer, they can still do it, but the default behavior is the good ole' FreeBSD > we all know and love. This is probably all well and good, but our adapter is a 10 Gb/s link and includes hardware CRC (actually two forms of this, LCRC on a per micropacket [32 byte] basis and ECRC over the entire message). Right now our goal is to see how fast we can get it to run on PC hardware on FreeBSD with IP. We don't really expect IP to allow us to reach it's theoretical limit of about 800 MB/s, but the closer we can get the better. :-) (ST and a system with faster main memory and dual PCI-X busses should allow us to get much closer.) Bob > > --giorgos -- Bob Willcox Egotist, n.: bob@vieo.com A person of low taste, more interested in himself than me. Austin, TX -- Ambrose Bierce, "The Devil's Dictionary" To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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