Date: Sat, 3 Mar 2007 13:38:23 -0500 From: Andre Guibert de Bruet <andy@siliconlandmark.com> To: Peter Jeremy <peterjeremy@optushome.com.au> Cc: freebsd-current@freebsd.org, Andrew Gallatin <gallatin@cs.duke.edu> Subject: Re: excessive TCP duplicate acks? Message-ID: <20DDE355-5F52-4E1F-B316-D933C816DE3B@siliconlandmark.com> In-Reply-To: <20070303000125.GA9918@turion.vk2pj.dyndns.org> References: <17850.13146.266196.499166@grasshopper.cs.duke.edu> <20070303000125.GA9918@turion.vk2pj.dyndns.org>
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On Mar 2, 2007, at 7:01 PM, Peter Jeremy wrote: > On 2007-Jan-26 11:59:06 -0500, Andrew Gallatin > <gallatin@cs.duke.edu> wrote: >> When running some benchmarks, I noticed tons of duplicate acks >> showing >> up in systat -tcp (thousands, or tens of thousands per second). > > Whilst investigating other problems, I've just seen the same on 6.2. > The following trace was taken on 192.168.234.1, which is running > 6.2-RELEASE/i386 (with ipfilter enabled) with fxp (Intel 82559) NICs. > 192.168.234.64 is running 6.2-STABLE/amd64 from late January (no > firewall active) with a bge (Broadcom BCM5705 A3, ASIC rev. 0x3003) > NIC and checksum offloading enabled. > > The multiple SYN packets are due to a bug in the IPfilter state > management, though it eventually allows a SYN through. (And it is not > totally unrealistic for multiple SYNs to be required before a SYN-ACK > is received so this does not excuse the ACK flood). Note that the > duplicate ACKs are being sent from the host without a firewall so this > does not appear to be related to ipfilter (or kern/102653). > > The common factor seems to be amd64. I am seeing this problem on a machine with dual 64-bit Xeons in i386 mode: Vendor ID: "GenuineIntel"; CPUID level 5 Intel-specific functions: Version 00000f34: Type 0 - Original OEM Family 15 - Pentium 4 Extended family 0 Model 3 - Intel Pentium 4 processor (generic) or newer Stepping 4 Reserved 0 Extended brand string: " Intel(R) Xeon(TM) CPU 3.00GHz" CLFLUSH instruction cache line size: 8 Hyper threading siblings: 1 Andy /* Andre Guibert de Bruet * 6f43 6564 7020 656f 2e74 4220 7469 6a20 */ /* Code poet / Sysadmin * 636f 656b 2e79 5320 7379 6461 696d 2e6e */ /* GSM: +1 734 846 8758 * 5520 494e 2058 6c73 7565 6874 002e 0000 */ /* WWW: siliconlandmark.com * C/C++, Java, Perl, PHP, SQL, XHTML, XML */
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