Date: Thu, 29 May 2008 16:25:33 +0200 From: Arnaud Houdelette <arnaud.houdelette@tzim.net> To: freebsd-stable@freebsd.org Subject: Bad TCP performance with large MTU on 7-stable. Message-ID: <483EBCDD.2070408@tzim.net>
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I got really poor performance when I try to upload files to the box (via pureFTP or Samba) when using jumbo frames somewhat above 2k. uname -a : FreeBSD carenath.tzim.net 7.0-STABLE FreeBSD 7.0-STABLE #4: Wed May 28 17:45:14 CEST 2008 tzim@carenath.tzim.net:/usr/obj/usr/src/sys/CARENATH amd64 It seems that TCP acks are delayed for about a second, so the upload rate nevers goes above 60kB/s. I can provide wireshark captures done on the box uploading the files if necessary. The client is a Windows XP64 box, but I do not recall having the same problem on 6.2. I did got about 100 MB/s for similar file transfers, but I had to disable jumbo frames when I upgraded to 7.0-Release because of some bug on txcsum/rxcsum on re(4) so I only noticed the issue recently. The txcsum bug doesn't seem to occur anymore, but now I have this strange rate issue, with or without checksum offloading disabled. I also tried with tso disabled. Same results. Is it related to the re(4) driver ? Or to the TCP stack ? Arnaud Houdelette
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