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/Documentation/networking/cxgb.txt

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  1                 Chelsio N210 10Gb Ethernet Network Controller
  2
  3                         Driver Release Notes for Linux
  4
  5                                 Version 2.1.1
  6
  7                                 June 20, 2005
  8
  9CONTENTS
 10========
 11 INTRODUCTION
 12 FEATURES
 13 PERFORMANCE
 14 DRIVER MESSAGES
 15 KNOWN ISSUES
 16 SUPPORT
 17
 18
 19INTRODUCTION
 20============
 21
 22 This document describes the Linux driver for Chelsio 10Gb Ethernet Network
 23 Controller. This driver supports the Chelsio N210 NIC and is backward
 24 compatible with the Chelsio N110 model 10Gb NICs.
 25
 26
 27FEATURES
 28========
 29
 30 Adaptive Interrupts (adaptive-rx)
 31 ---------------------------------
 32
 33  This feature provides an adaptive algorithm that adjusts the interrupt
 34  coalescing parameters, allowing the driver to dynamically adapt the latency
 35  settings to achieve the highest performance during various types of network
 36  load.
 37
 38  The interface used to control this feature is ethtool. Please see the
 39  ethtool manpage for additional usage information.
 40
 41  By default, adaptive-rx is disabled.
 42  To enable adaptive-rx:
 43
 44      ethtool -C <interface> adaptive-rx on
 45
 46  To disable adaptive-rx, use ethtool:
 47
 48      ethtool -C <interface> adaptive-rx off
 49
 50  After disabling adaptive-rx, the timer latency value will be set to 50us.
 51  You may set the timer latency after disabling adaptive-rx:
 52
 53      ethtool -C <interface> rx-usecs <microseconds>
 54
 55  An example to set the timer latency value to 100us on eth0:
 56
 57      ethtool -C eth0 rx-usecs 100
 58
 59  You may also provide a timer latency value while disabling adaptive-rx:
 60
 61      ethtool -C <interface> adaptive-rx off rx-usecs <microseconds>
 62
 63  If adaptive-rx is disabled and a timer latency value is specified, the timer
 64  will be set to the specified value until changed by the user or until
 65  adaptive-rx is enabled.
 66
 67  To view the status of the adaptive-rx and timer latency values:
 68
 69      ethtool -c <interface>
 70
 71
 72 TCP Segmentation Offloading (TSO) Support
 73 -----------------------------------------
 74
 75  This feature, also known as "large send", enables a system's protocol stack
 76  to offload portions of outbound TCP processing to a network interface card
 77  thereby reducing system CPU utilization and enhancing performance.
 78
 79  The interface used to control this feature is ethtool version 1.8 or higher.
 80  Please see the ethtool manpage for additional usage information.
 81
 82  By default, TSO is enabled.
 83  To disable TSO:
 84
 85      ethtool -K <interface> tso off
 86
 87  To enable TSO:
 88
 89      ethtool -K <interface> tso on
 90
 91  To view the status of TSO:
 92
 93      ethtool -k <interface>
 94
 95
 96PERFORMANCE
 97===========
 98
 99 The following information is provided as an example of how to change system
100 parameters for "performance tuning" an what value to use. You may or may not
101 want to change these system parameters, depending on your server/workstation
102 application. Doing so is not warranted in any way by Chelsio Communications,
103 and is done at "YOUR OWN RISK". Chelsio will not be held responsible for loss
104 of data or damage to equipment.
105
106 Your distribution may have a different way of doing things, or you may prefer
107 a different method. These commands are shown only to provide an example of
108 what to do and are by no means definitive.
109
110 Making any of the following system changes will only last until you reboot
111 your system. You may want to write a script that runs at boot-up which
112 includes the optimal settings for your system.
113
114  Setting PCI Latency Timer:
115      setpci -d 1425:* 0x0c.l=0x0000F800
116
117  Disabling TCP timestamp:
118      sysctl -w net.ipv4.tcp_timestamps=0
119
120  Disabling SACK:
121      sysctl -w net.ipv4.tcp_sack=0
122
123  Setting large number of incoming connection requests:
124      sysctl -w net.ipv4.tcp_max_syn_backlog=3000
125
126  Setting maximum receive socket buffer size:
127      sysctl -w net.core.rmem_max=1024000
128
129  Setting maximum send socket buffer size:
130      sysctl -w net.core.wmem_max=1024000
131
132  Set smp_affinity (on a multiprocessor system) to a single CPU:
133      echo 1 > /proc/irq/<interrupt_number>/smp_affinity
134
135  Setting default receive socket buffer size:
136      sysctl -w net.core.rmem_default=524287
137
138  Setting default send socket buffer size:
139      sysctl -w net.core.wmem_default=524287
140
141  Setting maximum option memory buffers:
142      sysctl -w net.core.optmem_max=524287
143
144  Setting maximum backlog (# of unprocessed packets before kernel drops):
145      sysctl -w net.core.netdev_max_backlog=300000
146
147  Setting TCP read buffers (min/default/max):
148      sysctl -w net.ipv4.tcp_rmem="10000000 10000000 10000000"
149
150  Setting TCP write buffers (min/pressure/max):
151      sysctl -w net.ipv4.tcp_wmem="10000000 10000000 10000000"
152
153  Setting TCP buffer space (min/pressure/max):
154      sysctl -w net.ipv4.tcp_mem="10000000 10000000 10000000"
155
156  TCP window size for single connections:
157   The receive buffer (RX_WINDOW) size must be at least as large as the
158   Bandwidth-Delay Product of the communication link between the sender and
159   receiver. Due to the variations of RTT, you may want to increase the buffer
160   size up to 2 times the Bandwidth-Delay Product. Reference page 289 of
161   "TCP/IP Illustrated, Volume 1, The Protocols" by W. Richard Stevens.
162   At 10Gb speeds, use the following formula:
163       RX_WINDOW >= 1.25MBytes * RTT(in milliseconds)
164       Example for RTT with 100us: RX_WINDOW = (1,250,000 * 0.1) = 125,000
165   RX_WINDOW sizes of 256KB - 512KB should be sufficient.
166   Setting the min, max, and default receive buffer (RX_WINDOW) size:
167       sysctl -w net.ipv4.tcp_rmem="<min> <default> <max>"
168
169  TCP window size for multiple connections:
170   The receive buffer (RX_WINDOW) size may be calculated the same as single
171   connections, but should be divided by the number of connections. The
172   smaller window prevents congestion and facilitates better pacing,
173   especially if/when MAC level flow control does not work well or when it is
174   not supported on the machine. Experimentation may be necessary to attain
175   the correct value. This method is provided as a starting point for the
176   correct receive buffer size.
177   Setting the min, max, and default receive buffer (RX_WINDOW) size is
178   performed in the same manner as single connection.
179
180
181DRIVER MESSAGES
182===============
183
184 The following messages are the most common messages logged by syslog. These
185 may be found in /var/log/messages.
186
187  Driver up:
188     Chelsio Network Driver - version 2.1.1
189
190  NIC detected:
191     eth#: Chelsio N210 1x10GBaseX NIC (rev #), PCIX 133MHz/64-bit
192
193  Link up:
194     eth#: link is up at 10 Gbps, full duplex
195
196  Link down:
197     eth#: link is down
198
199
200KNOWN ISSUES
201============
202
203 These issues have been identified during testing. The following information
204 is provided as a workaround to the problem. In some cases, this problem is
205 inherent to Linux or to a particular Linux Distribution and/or hardware
206 platform.
207
208  1. Large number of TCP retransmits on a multiprocessor (SMP) system.
209
210      On a system with multiple CPUs, the interrupt (IRQ) for the network
211      controller may be bound to more than one CPU. This will cause TCP
212      retransmits if the packet data were to be split across different CPUs
213      and re-assembled in a different order than expected.
214
215      To eliminate the TCP retransmits, set smp_affinity on the particular
216      interrupt to a single CPU. You can locate the interrupt (IRQ) used on
217      the N110/N210 by using ifconfig:
218          ifconfig <dev_name> | grep Interrupt
219      Set the smp_affinity to a single CPU:
220          echo 1 > /proc/irq/<interrupt_number>/smp_affinity
221
222      It is highly suggested that you do not run the irqbalance daemon on your
223      system, as this will change any smp_affinity setting you have applied.
224      The irqbalance daemon runs on a 10 second interval and binds interrupts
225      to the least loaded CPU determined by the daemon. To disable this daemon:
226          chkconfig --level 2345 irqbalance off
227
228      By default, some Linux distributions enable the kernel feature,
229      irqbalance, which performs the same function as the daemon. To disable
230      this feature, add the following line to your bootloader:
231          noirqbalance
232
233          Example using the Grub bootloader:
234              title Red Hat Enterprise Linux AS (2.4.21-27.ELsmp)
235              root (hd0,0)
236              kernel /vmlinuz-2.4.21-27.ELsmp ro root=/dev/hda3 noirqbalance
237              initrd /initrd-2.4.21-27.ELsmp.img
238
239  2. After running insmod, the driver is loaded and the incorrect network
240     interface is brought up without running ifup.
241
242      When using 2.4.x kernels, including RHEL kernels, the Linux kernel
243      invokes a script named "hotplug". This script is primarily used to
244      automatically bring up USB devices when they are plugged in, however,
245      the script also attempts to automatically bring up a network interface
246      after loading the kernel module. The hotplug script does this by scanning
247      the ifcfg-eth# config files in /etc/sysconfig/network-scripts, looking
248      for HWADDR=<mac_address>.
249
250      If the hotplug script does not find the HWADDRR within any of the
251      ifcfg-eth# files, it will bring up the device with the next available
252      interface name. If this interface is already configured for a different
253      network card, your new interface will have incorrect IP address and
254      network settings.
255
256      To solve this issue, you can add the HWADDR=<mac_address> key to the
257      interface config file of your network controller.
258
259      To disable this "hotplug" feature, you may add the driver (module name)
260      to the "blacklist" file located in /etc/hotplug. It has been noted that
261      this does not work for network devices because the net.agent script
262      does not use the blacklist file. Simply remove, or rename, the net.agent
263      script located in /etc/hotplug to disable this feature.
264
265  3. Transport Protocol (TP) hangs when running heavy multi-connection traffic
266     on an AMD Opteron system with HyperTransport PCI-X Tunnel chipset.
267
268      If your AMD Opteron system uses the AMD-8131 HyperTransport PCI-X Tunnel
269      chipset, you may experience the "133-Mhz Mode Split Completion Data
270      Corruption" bug identified by AMD while using a 133Mhz PCI-X card on the
271      bus PCI-X bus.
272
273      AMD states, "Under highly specific conditions, the AMD-8131 PCI-X Tunnel
274      can provide stale data via split completion cycles to a PCI-X card that
275      is operating at 133 Mhz", causing data corruption.
276
277      AMD's provides three workarounds for this problem, however, Chelsio
278      recommends the first option for best performance with this bug:
279
280        For 133Mhz secondary bus operation, limit the transaction length and
281        the number of outstanding transactions, via BIOS configuration
282        programming of the PCI-X card, to the following:
283
284           Data Length (bytes): 1k
285           Total allowed outstanding transactions: 2
286
287      Please refer to AMD 8131-HT/PCI-X Errata 26310 Rev 3.08 August 2004,
288      section 56, "133-MHz Mode Split Completion Data Corruption" for more
289      details with this bug and workarounds suggested by AMD.
290
291      It may be possible to work outside AMD's recommended PCI-X settings, try
292      increasing the Data Length to 2k bytes for increased performance. If you
293      have issues with these settings, please revert to the "safe" settings
294      and duplicate the problem before submitting a bug or asking for support.
295
296      NOTE: The default setting on most systems is 8 outstanding transactions
297            and 2k bytes data length.
298
299  4. On multiprocessor systems, it has been noted that an application which
300     is handling 10Gb networking can switch between CPUs causing degraded
301     and/or unstable performance.
302
303      If running on an SMP system and taking performance measurements, it
304      is suggested you either run the latest netperf-2.4.0+ or use a binding
305      tool such as Tim Hockin's procstate utilities (runon)
306      <http://www.hockin.org/~thockin/procstate/>.
307
308      Binding netserver and netperf (or other applications) to particular
309      CPUs will have a significant difference in performance measurements.
310      You may need to experiment which CPU to bind the application to in
311      order to achieve the best performance for your system.
312
313      If you are developing an application designed for 10Gb networking,
314      please keep in mind you may want to look at kernel functions
315      sched_setaffinity & sched_getaffinity to bind your application.
316
317      If you are just running user-space applications such as ftp, telnet,
318      etc., you may want to try the runon tool provided by Tim Hockin's
319      procstate utility. You could also try binding the interface to a
320      particular CPU: runon 0 ifup eth0
321
322
323SUPPORT
324=======
325
326 If you have problems with the software or hardware, please contact our
327 customer support team via email at support@chelsio.com or check our website
328 at http://www.chelsio.com
329
330===============================================================================
331
332 Chelsio Communications
333 370 San Aleso Ave.
334 Suite 100
335 Sunnyvale, CA 94085
336 http://www.chelsio.com
337
338This program is free software; you can redistribute it and/or modify
339it under the terms of the GNU General Public License, version 2, as
340published by the Free Software Foundation.
341
342You should have received a copy of the GNU General Public License along
343with this program; if not, write to the Free Software Foundation, Inc.,
34459 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
345
346THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED
347WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
348MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
349
350 Copyright (c) 2003-2005 Chelsio Communications. All rights reserved.
351
352===============================================================================