Date: Mon, 27 Jun 2005 08:31:01 -0700 From: Luigi Rizzo <rizzo@icir.org> To: Ruslan Ermilov <ru@FreeBSD.org> Cc: cvs-src@FreeBSD.org, Gleb Smirnoff <glebius@FreeBSD.org>, cvs-all@FreeBSD.org, src-committers@FreeBSD.org Subject: Re: cvs commit: src/sys/netinet/libalias alias_ftp.c alias_irc.c alias_local.h alias_proxy.c alias_skinny.c alias_smedia.c alias_util.c Message-ID: <20050627083101.B56456@xorpc.icir.org> In-Reply-To: <20050627152155.GF93072@ip.net.ua>; from ru@FreeBSD.org on Mon, Jun 27, 2005 at 06:21:55PM %2B0300 References: <200506270736.j5R7a3OZ036531@repoman.freebsd.org> <20050627152155.GF93072@ip.net.ua>
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On Mon, Jun 27, 2005 at 06:21:55PM +0300, Ruslan Ermilov wrote: ... > Why can't we just say that checksum offloading is incompatible > with NAT (like with many other things), and do the software > checksum calculations in libalias? actually the more i see it the more i think checksum offloading is a disgrace rather than a performance boost. it needs a lot of special cases throughout the protocol stack to be supported properly, which constitutes extra overhead with low-end hardware which does not support the offloading; it does not pay on small packets such as acks where you have to touch the whole packet anyways; some hardware needs the checksum engine to be reprogrammed when changing protocol type (tcp <-> udp) which require extra I/O cycles on the bus that are expensive; some hardware has broken checksum engines; cheers luigi
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