Date: Thu, 22 May 2003 23:11:30 -0700 (PDT) From: Don Lewis <truckman@FreeBSD.org> To: wpaul@FreeBSD.org Cc: current@FreeBSD.org Subject: Re: possible bug fix for 82550-based fxp packet truncation problem Message-ID: <200305230611.h4N6BUM7077910@gw.catspoiler.org> In-Reply-To: <20030523003333.E83B537B401@hub.freebsd.org>
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On 22 May, Bill Paul wrote: >> Don Lewis <truckman@freebsd.org> wrote >> in <200305220823.h4M8N9M7075271@gw.catspoiler.org>: >> >> truckman> If you are using one of my previous patches which worked around the >> truckman> problem by disabling the IPCB mode, you may want to try the patch below. >> >> This works fine in my environment. My fxp has the following id: >> >> fxp0@pci7:2:0: class=0x020000 card=0x10508086 chip=0x12298086 rev=0x0d hdr=0x00 >> >> Without any patches, packets whose size is 216+(N*1480) are dropped >> as I reported on -stable before. Similarly I tried "ping -s X" with >> various payload size from X=1 to X=6000 in the system using the >> patched kernel, but no error is reported. >> > > Just to let people know, I have been trying to investigate this, but > my time has been somewhat limited lately. The original reason I turned > off the IP checksumming on transmit was that there was one test case > where the chip seemed to be generating improper checksums. That is, > if you did something like: ping -s 1473 <otherhost>. This would result > in a full sized frame, plus a small IP fragment containing just one > byte of data. On the machine I used for testing, the small fragment > was rejected by the host on the other side due to a bad header checksum. According to the second note in the Intel document that I cited, hardware checksumming is unsupported in this case. > The machine I was testing on was an old Gateway 2000 Pentium 166 system. > I have since tried re-enabling the IP checksumming on transmit and > re-run the test on an Athlon system, and everything works correctly. > (Coincidentally, I ran a similar test on a PowerPC 440GP board running > VxWorks and everything worked correctly there too.) > > So my theory is that the original bug I found was not due to the chip > computing bad checksums, although I'm at a loss to say what the cause > really was. And I don't have that particular machine handy anymore. :/ Maybe the stack was fixed to not request hardware IP header checksumming if the card doesn't advertise support for checksumming fragments ... > As an experiment, you might try re-enabling the IP header checksumming to > see just what happens. If the ping -s 1473 tests succeeds, then maybe > I was smoking crack and we should turn IP checksumming back on. Sounds like a good task for after 5.1-RELEASE. I'm just hoping to get the existing driver fixed before 5.1-RELEASE so that it doesn't truncate packets like it currently does.
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