Date: Tue, 18 Aug 2009 10:33:57 -0600 From: Manish Vachharajani <manishv@lineratesystems.com> To: freebsd-stable@freebsd.org Subject: Dropped vs. missed packets in the ixgbe driver Message-ID: <5bc218350908180933q22e7dc22s835fd54f35ca764b@mail.gmail.com> In-Reply-To: <5bc218350908171524m5a46c3dbm3e6af625c51370d0@mail.gmail.com> References: <5bc218350908171524m5a46c3dbm3e6af625c51370d0@mail.gmail.com>
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I've been doing some performance testing on freebsd 7.2 and noticed that the ixgbe driver does not report missed packets as dropped when queried via netstat -id (the ixgbe driver in the 8.0 =A0beta has a similar issue). =A0A missed packet is a packet that was correctly received by the NIC but because it was out of descriptors and internal memory, the packet had to be dropped by the NIC itself -- a hardware register counts such events. =A0Instead the driver only reports drops that are due to the driver itself, i.e., the NIC DMAed the packet to memory but the driver had to drop something because it was out of mbufs. =A0Is the miss count reported elsewhere (besides via a kernel printf from the driver)? =A0At the end of the email I give a stats dump from the driver and from netstat, note the number of packets dropped is 0 as reported by netstat but the Missed field in the dmesg output shows many missed packets. >From my perspective, it is disconcerting to see performance degradation on the link, along with TCP ack retransmits, packet reordering, etc. (on a point-to-point link with no switch in between) but then see no drops reported by netstat because the driver didn't drop the packet, the NIC did. =A0The fix should be straight-forward and I'll gladly make a patch assuming that it is indeed a bug and not a conscious design choice. Here is the relevant netstat output Name =A0 =A0Mtu Network =A0 =A0 =A0 Address =A0 =A0 =A0 =A0 =A0 =A0 =A0Ipkt= s Ierrs =A0 =A0Opkts Oerrs =A0Coll Drop ix0 =A0 =A01500 <Link#1> =A0 =A0 =A000:30:48:94:60:ec =A0 =A0 =A0 =A00 =A0 = =A0 0 =A0 =A0 =A0 =A01 =A00 =A0 =A0 0 =A0 =A00 ix0 =A0 =A01500 192.168.105.0 192.168.105.2 =A0 =A0 =A0 =A0 =A0 =A00 =A0 = =A0 - =A0 =A0 =A0 =A00 =A0- =A0 =A0 - =A0 =A0- ix1 =A0 =A01500 <Link#2> =A0 =A0 =A000:30:48:94:60:ed =A0 =A0 =A011M =A0 = =A0 0 =A0 =A0 6.1M =A00 =A0 =A0 0 =A0 =A00 ix1 =A0 =A01500 192.168.5.0 =A0 192.168.5.2 =A0 =A0 =A0 =A0 =A0 =A010M =A0 = =A0 - =A0 =A0 6.1M =A0- =A0 =A0 - =A0 =A0- And here is the dmesg output after doing a sysctl dev.ix.1.stats=3D1 ix1: Std Mbuf Failed =3D 0 ix1: Missed Packets =3D 413872 ix1: Receive length errors =3D 0 ix1: Crc errors =3D 0 ix1: Driver dropped packets =3D 0 ix1: watchdog timeouts =3D 0 ix1: XON Rcvd =3D 616428212235 ix1: XON Xmtd =3D 0 ix1: XOFF Rcvd =3D 616428212235 ix1: XOFF Xmtd =3D 0 ix1: Total Packets Rcvd =3D 12424533 ix1: Good Packets Rcvd =3D 12010661 ix1: Good Packets Xmtd =3D 6419128 ix1: TSO Transmissions =3D 0 Manish -- Manish Vachharajani manishv@lineratesystems.com
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