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Small Packet Traffic Performance Optimization for 8255x and 8254x Ethernet Controllers

Application Note (AP-453) Revision 1.0 September 2003 Revision History Revision 1.0 Date Sep 2003 Initial release. Description INFORMATION IN THIS DOCUMENT IS PROVIDED IN CONNECTION WITH INTEL® PRODUCTS. NO LICENSE, EXPRESS OR IMPLIED, BY ESTOPPEL OR OTHERWISE, TO ANY INTELLECTUAL PROPERTY RIGHTS IS GRANTED BY THIS DOCUMENT. EXCEPT AS PROVIDED IN INTEL'S TERMS AND CONDITIONS OF SALE FOR SUCH PRODUCTS, INTEL ASSUMES NO LIABILITY WHATSOEVER, AND INTEL DISCLAIMS ANY EXPRESS OR IMPLIED WARRANTY, RELATING TO SALE AND/OR USE OF INTEL PRODUCTS INCLUDING LIABILITY OR WARRANTIES RELATING TO FITNESS FOR A PARTICULAR PURPOSE, MERCHANTABILITY, OR INFRINGEMENT OF ANY PATENT, COPYRIGHT OR OTHER INTELLECTUAL PROPERTY RIGHT. Intel products are not intended for use in medical, life saving, life sustaining applications. Intel may make changes to specifications and product descriptions at any time, without notice. Designers must not rely on the absence or characteristics of any features or instructions marked "reserved" or "undefined." Intel reserves these for future definition and shall have no responsibility whatsoever for conflicts or incompatibilities arising from future changes to them. The Intel product(s) described in this document may contain design defects or errors known as errata which may cause the product to deviate from published specifications. Current characterized errata are available on request. Copies of documents which have an ordering number and are referenced in this document, or other Intel literature may be obtained by calling 1-800- 548-4725 or by visiting Intel's website at http://www.intel.com. Copyright © 2003, Intel Corporation. *Third-party brands and names are the property of their respective owners. Application Note (AP-453) Small Packet Traffic Performance Optimization for 8255x and 8254x Ethernet Controllers Contents 1.0 1.1 1.2 2.0 Introduction.........................................................................................................................1 Scope............................................................................................................................................1 Reference Documents..................................................................................................................1 Performance Defined .........................................................................................................3 3.0 Small Packet Performance Issues .....................................................................................5 3.1 Tradeoffs Inherent in Small Packet Performance.........................................................................5 3.2 Network Protocol Overhead..........................................................................................................5 3.3 Network Protocol Behavior ...........................................................................................................7 3.4 Per Packet Processing Overhead.................................................................................................7 3.4.1 Application Related Overhead .........................................................................................8 3.4.2 Interrupt Latency Considerations.....................................................................................9 3.5 System Bus Limitations ................................................................................................................9 4.0 Optimization Strategies for 8254x and 8255x Ethernet Controllers .................................11 4.1 Increase Receive Resources Available to the Controller............................................................11 4.2 Optimize Interrupt Moderation ....................................................................................................11 4.3 Packet Data Polling ....................................................................................................................12 4.4 Use Simplified Mode (8255x-based controllers only) .................................................................12 5.0 Other Design Recommendations .....................................................................................15 5.1 Coalesce Small Fragments into Contiguous Buffers ..................................................................15 5.2 Kernel vs User Space.................................................................................................................15 5.3 Hot-Spot Optimizations...............................................................................................................15 5.4 Buffer Allocation Optimizations...................................................................................................15 5.5 Discarding Packets and Flow Control Schemes.........................................................................16 Figures 1 Typical TCP/IP Ethernet Frame....................................................................................................6 2 Frame Size vs. Maximum Throughput for 1Gb/s Unidirectional Traffic ........................................6 3 Interrupts Per Second for Different Packet Size...........................................................................8 4 CPU Utilization with Many System Calls and 64-byte Segments (Linux OS) ...............................8 5 CPU Utilization with Few System Calls and 64-byte Segments (Linux OS) .................................9 6 PCI Bus Transaction Overhead..................................................................................................10 Tables 1 Throughput Calculations for Unidirectional Gigabit Traffic ...........................................................6 Application Note (AP-453) 1 Small Packet Traffic Performance Optimization for 8255x and 8254x Ethernet Controllers Note: This page is intentionally left blank. 2 Application Note (AP-453) 1.0 1.1 1.2 Small Packet Traffic Performance Optimization for 8255x and 8254x Ethernet Controllers Introduction Scope This document discusses the "small packet" performance of Read the full Small Packet Traffic Performance Optimization for 8255x and 8254x Ethernet Controllers.

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