Date: Thu, 15 Sep 2016 18:53:25 +0000 From: bugzilla-noreply@freebsd.org To: freebsd-net@FreeBSD.org Subject: [Bug 208803] ixgbe(4) reports wrong IPv4 checksum when txcsum is enabled Message-ID: <bug-208803-2472-1PFAPk09di@https.bugs.freebsd.org/bugzilla/> In-Reply-To: <bug-208803-2472@https.bugs.freebsd.org/bugzilla/> References: <bug-208803-2472@https.bugs.freebsd.org/bugzilla/>
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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=3D208803 Jeb Cramer <cramerj@intel.com> changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |cramerj@intel.com --- Comment #3 from Jeb Cramer <cramerj@intel.com> --- I'm not understanding what the bug is here. tcpdump, on the transmit side, captures packets before they reach the hardware. If hardware checksum offloading is enabled, the checksum value as reported by the stack (and thus tcpdump) is bogus because the stack didn't do the calculation. The hardware will take care of the checksum when the stack passes the packet to the hard= ware (via the driver). If you're concerned about the difference between FreeBSD and Linux, that mi= ght be worth exploring for future performance enhancements of the stack, if it makes sense. The Linux networking stack seems to calculate IPv4 checksums, regardless. And that would be why the checksum is reported correctly on tcpdump. A few memory reads...a couple folds for calculating the checksum...perhaps the number of instructions for this isn't too expensive = in their opinion? I don't know. I'm confused on #2. Are you seeing the same behavior as the 82598? Or are= you seeing the checksum reported correctly? If the former, then they probably = have the same hardware feature. If the latter, I don't have an answer. #3 isn't any different than the IPv4 case. Hardware will take care of the checksum calculation. --=20 You are receiving this mail because: You are the assignee for the bug.=
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