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+ Chelsio N210 10Gb Ethernet Network Controller
+ Driver Release Notes for Linux
+ Version 2.1.1
+ June 20, 2005
+ DRIVER MESSAGES
+ KNOWN ISSUES
+ This document describes the Linux driver for Chelsio 10Gb Ethernet Network
+ Controller. This driver supports the Chelsio N210 NIC and is backward
+ compatible with the Chelsio N110 model 10Gb NICs.
+ Adaptive Interrupts (adaptive-rx)
+ This feature provides an adaptive algorithm that adjusts the interrupt
+ coalescing parameters, allowing the driver to dynamically adapt the latency
+ settings to achieve the highest performance during various types of network
+ The interface used to control this feature is ethtool. Please see the
+ ethtool manpage for additional usage information.
+ By default, adaptive-rx is disabled.
+ To enable adaptive-rx:
+ ethtool -C <interface> adaptive-rx on
+ To disable adaptive-rx, use ethtool:
+ ethtool -C <interface> adaptive-rx off
+ After disabling adaptive-rx, the timer latency value will be set to 50us.
+ You may set the timer latency after disabling adaptive-rx:
+ ethtool -C <interface> rx-usecs <microseconds>
+ An example to set the timer latency value to 100us on eth0:
+ ethtool -C eth0 rx-usecs 100
+ You may also provide a timer latency value while disabling adaptive-rx:
+ ethtool -C <interface> adaptive-rx off rx-usecs <microseconds>
+ If adaptive-rx is disabled and a timer latency value is specified, the timer
+ will be set to the specified value until changed by the user or until
+ adaptive-rx is enabled.
+ To view the status of the adaptive-rx and timer latency values:
+ ethtool -c <interface>
+ TCP Segmentation Offloading (TSO) Support
+ This feature, also known as "large send", enables a system's protocol stack
+ to offload portions of outbound TCP processing to a network interface card
+ thereby reducing system CPU utilization and enhancing performance.
+ The interface used to control this feature is ethtool version 1.8 or higher.
+ Please see the ethtool manpage for additional usage information.
+ By default, TSO is enabled.
+ To disable TSO:
+ ethtool -K <interface> tso off
+ To enable TSO:
+ ethtool -K <interface> tso on
+ To view the status of TSO:
+ ethtool -k <interface>
+ The following information is provided as an example of how to change system
+ parameters for "performance tuning" an what value to use. You may or may not
+ want to change these system parameters, depending on your server/workstation
+ application. Doing so is not warranted in any way by Chelsio Communications,
+ and is done at "YOUR OWN RISK". Chelsio will not be held responsible for loss
+ of data or damage to equipment.
+ Your distribution may have a different way of doing things, or you may prefer
+ a different method. These commands are shown only to provide an example of
+ what to do and are by no means definitive.
+ Making any of the following system changes will only last until you reboot
+ your system. You may want to write a script that runs at boot-up which
+ includes the optimal settings for your system.
+ Setting PCI Latency Timer:
+ setpci -d 1425:* 0x0c.l=0x0000F800
+ Disabling TCP timestamp:
+ sysctl -w net.ipv4.tcp_timestamps=0
+ Disabling SACK:
+ sysctl -w net.ipv4.tcp_sack=0
+ Setting large number of incoming connection requests:
+ sysctl -w net.ipv4.tcp_max_syn_backlog=3000
+ Setting maximum receive socket buffer size:
+ sysctl -w net.core.rmem_max=1024000
+ Setting maximum send socket buffer size:
+ sysctl -w net.core.wmem_max=1024000
+ Set smp_affinity (on a multiprocessor system) to a single CPU:
+ echo 1 > /proc/irq/<interrupt_number>/smp_affinity
+ Setting default receive socket buffer size:
+ sysctl -w net.core.rmem_default=524287
+ Setting default send socket buffer size:
+ sysctl -w net.core.wmem_default=524287
+ Setting maximum option memory buffers:
+ sysctl -w net.core.optmem_max=524287
+ Setting maximum backlog (# of unprocessed packets before kernel drops):
+ sysctl -w net.core.netdev_max_backlog=300000
+ Setting TCP read buffers (min/default/max):
+ sysctl -w net.ipv4.tcp_rmem="10000000 10000000 10000000"
+ Setting TCP write buffers (min/pressure/max):
+ sysctl -w net.ipv4.tcp_wmem="10000000 10000000 10000000"
+ Setting TCP buffer space (min/pressure/max):
+ sysctl -w net.ipv4.tcp_mem="10000000 10000000 10000000"
+ TCP window size for single connections:
+ The receive buffer (RX_WINDOW) size must be at least as large as the
+ Bandwidth-Delay Product of the communication link between the sender and
+ receiver. Due to the variations of RTT, you may want to increase the buffer
+ size up to 2 times the Bandwidth-Delay Product. Reference page 289 of
+ "TCP/IP Illustrated, Volume 1, The Protocols" by W. Richard Stevens.
+ At 10Gb speeds, use the following formula:
+ RX_WINDOW >= 1.25MBytes * RTT(in milliseconds)
+ Example for RTT with 100us: RX_WINDOW = (1,250,000 * 0.1) = 125,000
+ RX_WINDOW sizes of 256KB - 512KB should be sufficient.
+ Setting the min, max, and default receive buffer (RX_WINDOW) size:
+ sysctl -w net.ipv4.tcp_rmem="<min> <default> <max>"
+ TCP window size for multiple connections:
+ The receive buffer (RX_WINDOW) size may be calculated the same as single
+ connections, but should be divided by the number of connections. The
+ smaller window prevents congestion and facilitates better pacing,
+ especially if/when MAC level flow control does not work well or when it is
+ not supported on the machine. Experimentation may be necessary to attain
+ the correct value. This method is provided as a starting point for the
+ correct receive buffer size.
+ Setting the min, max, and default receive buffer (RX_WINDOW) size is
+ performed in the same manner as single connection.
+ The following messages are the most common messages logged by syslog. These
+ may be found in /var/log/messages.
+ Driver up:
+ Chelsio Network Driver - version 2.1.1
+ NIC detected:
+ eth#: Chelsio N210 1x10GBaseX NIC (rev #), PCIX 133MHz/64-bit
+ Link up:
+ eth#: link is up at 10 Gbps, full duplex
+ Link down:
+ eth#: link is down
+ These issues have been identified during testing. The following information
+ is provided as a workaround to the problem. In some cases, this problem is
+ inherent to Linux or to a particular Linux Distribution and/or hardware
+ 1. Large number of TCP retransmits on a multiprocessor (SMP) system.
+ On a system with multiple CPUs, the interrupt (IRQ) for the network
+ controller may be bound to more than one CPU. This will cause TCP
+ retransmits if the packet data were to be split across different CPUs
+ and re-assembled in a different order than expected.
+ To eliminate the TCP retransmits, set smp_affinity on the particular
+ interrupt to a single CPU. You can locate the interrupt (IRQ) used on
+ the N110/N210 by using ifconfig:
+ ifconfig <dev_name> | grep Interrupt
+ Set the smp_affinity to a single CPU:
+ echo 1 > /proc/irq/<interrupt_number>/smp_affinity
+ It is highly suggested that you do not run the irqbalance daemon on your
+ system, as this will change any smp_affinity setting you have applied.
+ The irqbalance daemon runs on a 10 second interval and binds interrupts
+ to the least loaded CPU determined by the daemon. To disable this daemon:
+ chkconfig --level 2345 irqbalance off
+ By default, some Linux distributions enable the kernel feature,
+ irqbalance, which performs the same function as the daemon. To disable
+ this feature, add the following line to your bootloader:
+ Example using the Grub bootloader:
+ title Red Hat Enterprise Linux AS (2.4.21-27.ELsmp)
+ root (hd0,0)
+ kernel /vmlinuz-2.4.21-27.ELsmp ro root=/dev/hda3 noirqbalance
+ initrd /initrd-2.4.21-27.ELsmp.img
+ 2. After running insmod, the driver is loaded and the incorrect network
+ interface is brought up without running ifup.
+ When using 2.4.x kernels, including RHEL kernels, the Linux kernel
+ invokes a script named "hotplug". This script is primarily used to
+ automatically bring up USB devices when they are plugged in, however,
+ the script also attempts to automatically bring up a network interface
+ after loading the kernel module. The hotplug script does this by scanning
+ the ifcfg-eth# config files in /etc/sysconfig/network-scripts, looking
+ for HWADDR=<mac_address>.
+ If the hotplug script does not find the HWADDRR within any of the
+ ifcfg-eth# files, it will bring up the device with the next available
+ interface name. If this interface is already configured for a different
+ network card, your new interface will have incorrect IP address and
+ network settings.
+ To solve this issue, you can add the HWADDR=<mac_address> key to the
+ interface config file of your network controller.
+ To disable this "hotplug" feature, you may add the driver (module name)
+ to the "blacklist" file located in /etc/hotplug. It has been noted that
+ this does not work for network devices because the net.agent script
+ does not use the blacklist file. Simply remove, or rename, the net.agent
+ script located in /etc/hotplug to disable this feature.
+ 3. Transport Protocol (TP) hangs when running heavy multi-connection traffic
+ on an AMD Opteron system with HyperTransport PCI-X Tunnel chipset.
+ If your AMD Opteron system uses the AMD-8131 HyperTransport PCI-X Tunnel
+ chipset, you may experience the "133-Mhz Mode Split Completion Data
+ Corruption" bug identified by AMD while using a 133Mhz PCI-X card on the
+ bus PCI-X bus.
+ AMD states, "Under highly specific conditions, the AMD-8131 PCI-X Tunnel
+ can provide stale data via split completion cycles to a PCI-X card that
+ is operating at 133 Mhz", causing data corruption.
+ AMD's provides three workarounds for this problem, however, Chelsio
+ recommends the first option for best performance with this bug:
+ For 133Mhz secondary bus operation, limit the transaction length and
+ the number of outstanding transactions, via BIOS configuration
+ programming of the PCI-X card, to the following:
+ Data Length (bytes): 1k
+ Total allowed outstanding transactions: 2
+ Please refer to AMD 8131-HT/PCI-X Errata 26310 Rev 3.08 August 2004,
+ section 56, "133-MHz Mode Split Completion Data Corruption" for more
+ details with this bug and workarounds suggested by AMD.
+ It may be possible to work outside AMD's recommended PCI-X settings, try
+ increasing the Data Length to 2k bytes for increased performance. If you
+ have issues with these settings, please revert to the "safe" settings
+ and duplicate the problem before submitting a bug or asking for support.
+ NOTE: The default setting on most systems is 8 outstanding transactions
+ and 2k bytes data length.
+ 4. On multiprocessor systems, it has been noted that an application which
+ is handling 10Gb networking can switch between CPUs causing degraded
+ and/or unstable performance.
+ If running on an SMP system and taking performance measurements, it
+ is suggested you either run the latest netperf-2.4.0+ or use a binding
+ tool such as Tim Hockin's procstate utilities (runon)
+ Binding netserver and netperf (or other applications) to particular
+ CPUs will have a significant difference in performance measurements.
+ You may need to experiment which CPU to bind the application to in
+ order to achieve the best performance for your system.
+ If you are developing an application designed for 10Gb networking,
+ please keep in mind you may want to look at kernel functions
+ sched_setaffinity & sched_getaffinity to bind your application.
+ If you are just running user-space applications such as ftp, telnet,
+ etc., you may want to try the runon tool provided by Tim Hockin's
+ procstate utility. You could also try binding the interface to a
+ particular CPU: runon 0 ifup eth0
+ If you have problems with the software or hardware, please contact our
+ customer support team via email at firstname.lastname@example.org or check our website
+ at http://www.chelsio.com
+ Chelsio Communications
+ 370 San Aleso Ave.
+ Suite 100
+ Sunnyvale, CA 94085
+This program is free software; you can redistribute it and/or modify
+it under the terms of the GNU General Public License, version 2, as
+published by the Free Software Foundation.
+You should have received a copy of the GNU General Public License along
+with this program; if not, write to the Free Software Foundation, Inc.,
+59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED
+WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
+MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
+ Copyright (c) 2003-2005 Chelsio Communications. All rights reserved.