Руководство По Проектированию для Cisco Cisco Nexus 5010 Switch

 

Design Guide 

 

© 2010 Cisco Systems, Inc. All rights reserved. This document is Cisco Public Information. 

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For more information about TCP chimney and RSS, refer to the following publications: 

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The Microsoft Windows Server Scalable Network Pack controls these parameters (as well as others): 

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 This parameter is enabled in the registry editor as EnableTCPChimney = 1. If TCP 

chimney is not enabled, and if the full TCP stack is offloaded in the network adapter card, then TCP traffic has 
an oscillating behavior. If TCP chimney is enabled and the network adapter card has TCP offload disabled, 
then TCP traffic is dropped. 

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 This parameter allows distribution of the traffic to the cores that are present in the system. For example, 

with four cores, you should configure the driver for four queues, and you should configure EnableRSS = 1 in 
the registry editor. If RSS is not enabled, Microsoft Windows by default uses only one core for TCP/IP 
processing. 

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 This parameter is controlled in the registry by the setting called EnableTCPA = 1. This feature 

allows direct memory access between the adapter and the CPU. 

Some of these settings can be configured using the command-line interface (CLI) instead of the registry editor, 
providing the advantage of not requiring a reboot (the netsh CLI shows all the configurations available): 

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Microsoft Windows Server 2003: netsh int ip set chimney ENABLED 

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Microsoft Windows Server 2008: netsh int tcp set global chimney=enabled 

To verify that TCP chimney and hardware offloads are working, enter the command netstat –t. Connections listed as 

 are TCP offloaded by the NIC, and connections listed INHOST are handled by the CPU. 

Operating systems in general offer less performance in receive mode (traffic received by the server) than in transmit 
mode (traffic sent by the server), so in typical performance tests with two machines with identical hardware, the 
sender can easily overwhelm the receiver, causing it to drop frames. To make sure that the sender and receiver do 
not throttle the performance because of the drops, you should make sure that selective acknowledgement (SACK) is 
enabled in the adapter and the operating system. 

When you are operating with TCP offload disabled, the TCP/IP stack in Microsoft Windows automatically implements 
SACK. 

When you are operating with TCP offload enabled and the TCP/IP stack is implemented in hardware on the network 
adapter card, you may need to verify that SACK is enabled at the network adapter layer. 

Assume that you have a setup with a sender and receiver as follows: 

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 Four-core machine, 8 GB of RAM, running Microsoft Windows Server 2008 

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 Two-core machine, 4 GB of RAM, running Microsoft Windows Server 2003 

You have checked that the network adapters are plugged into an 8X slot, and you have enabled all the parameters 
on the driver as recommended in this chapter, but you reach a maximum performance of only approximately 4 Gbps. 

You check Windows Task Manager on host2 during the test. It shows that one of the two cores is used, but the 
second core is not (Figure 6).