Worldwide [change] |Account |Register |About Cisco
Guest

Hierarchical Navigation

IBM CIP Protocols

Channel Interface Processor TCP/IP Datagram Performance Tuning

Downloads

Document ID: 12331


Contents

Introduction
Before You Begin
      Conventions
      Prerequisites
      Components Used
General Tuning Summary
Tuning for Congestion
FTP Tuning Summary
Performance Tuning Parameters
      Packet Size or MTU
      Workstation Data Buffers/Window Size
      Host Data Buffers/Window Size
      Data Set Block Size
      File System Speed
      LAN Adapter Parameters
      DEFAULTNET (Gateway Statement)
      Tuning for Small Packets
AIX Performance Considerations
Adstar Distributed Storage Manager Performance Considerations
MVS TCP/IP Configuration Files
Related Information

Introduction

This document includes general items to consider when tuning Channel Interface Processor (CIP) TCP/IP datagram performance. This document is not meant as a specific guide to tune your system.

Before You Begin

Conventions

For more information on document conventions, see the Cisco Technical Tips Conventions.

Prerequisites

There are no specific prerequisites for this document.

Components Used

This document was originally written for the Multiple Virtual Storage (MVS) and Virtual Machine (VM) operating systems, however, most of the information is applicable to the OS/390 operating system.

General Tuning Summary

This section provides tips on tuning CIP TCP/IP performance.

  • Packet size/MTU (MVS and workstation) — Performance improves as packet size/MTU increases.

  • TCP/IP window size (MVS and workstation) — Performance improves as TCP/IP window size increases.

  • File system characteristics (such as cache, blksize, Direct Access Storage Device (DASD), for example) can greatly influence TCP/IP performance (CPU and throughput).

  • For best performance, use a cached or striped DASD .

  • LAN adapter type and settings (buffer sizes, SizWorkBuf, for example).

  • For slow lines, delay acknowledgements, and piggy-back on return.

  • For small partial packets, do not delay acknowledgements.

Tuning for Congestion

Multiple protocols running on slow lines can cause congestion. To avoid this:

  • Use smaller packets and smaller windows to slow down traffic.

  • Use a minimum of two packets per window for congestion control to work.

FTP Tuning Summary

This section provides tips on tuning FTP performance.

  • MVS CPU decreases as packet size/MTU increases.

  • MVS throughput increases and MVS CPU decreases as workstation window size increases. The recommended workstation window size is 32 KB.

  • MVS throughput increases and MVS CPU decreases as MVS TCP/IP data buffer size (TCP window) increases. The recommended MVS window size is 32 KB.

  • MVS throughput increases as MVS data set blocksize increases. The recommend blocksize is 1/2 track.

  • For best performance, set the checkpoint interval (CHKPTINT) parameter to zero (TCPIP.FTP.DATA).

  • File system characteristics (Cache, blksize, DASD, for example) can greatly influence FTP performance (CPU and throughput).

  • MVS FTP servers — Use multiple FTP servers or FTP server subtasks to increase FTP performance.

Performance Tuning Parameters

Packet Size or MTU

Packet size is also referred to as frame size or MTU. Packet size is defined for both client (workstation) and server (host).

  • For TCP/IP (VM/MVS), the term packet size is used. It is defined under the GATEWAY statements in the TCP/IP PROFILE. The default size is used if it is not explicitly defined.

  • For workstations (IBM OS/2 and Advanced Interface eXecutive (AIX) for the IBM RISC/6000), the term MTU is used. It is defined by issuing the ifconfig command.

  • Packet size is determined during connection establishment between client and server. The smaller of the two is used as the packet size for data transfer between the client and server.

  • The MTU for Ethernet, Fiber Distributed Data Interface (FDDI), and Token Ring can be used as follows:

    Ethernet (1500), FDDI (4 KB), and Token Ring (4 KB). The TCP Maximum Segment Size (MSS) may also need to be considered when configuring the MTU size. The MSS + the IP header must be less than or equal to the MTU or fragmentation occurs.

Workstation Data Buffers/Window Size

  • Workstation data buffers for the IBM RISC/6000 are defined using network option command (no -o).

  • The default size is 16 KB for the IBM RISC/6000 with AIX Version 3.2.

  • For setting 32 KB send and receive buffers, issue the following commands:

    no -o tcp_sendspace=32768 -o tcp_recvspace=32768   
no -o udp_sendspace=32768 -o udp_recvspace=32768

Host Data Buffers/Window Size

  • For TCP/IP (MVS/VM), Host data buffer size is defined in the TCP/IP PROFILE.

  • The statement is DATABUFFERPOOLSIZE x y , where x indicates the number of buffers and y indicates the size of the buffers. The defaults are 160 for the number of buffers and 8192 (or 16384 with MVS TCP/IP V3RI PTF # PN70195) for the size of the buffers.

  • The recommended data buffer size for file transfer is 32768 for CIP TCP/IP DATAGRAM and OFFLOAD.

Data Set Block Size

  • The recommended data set block size for MVS is 1/2 DASD track.

  • For IBM 3380s, 1/2 DASD track is 23440 bytes. For IBM 3390s and 9334s, 1/2 DASD track is 29 KB bytes.

File System Speed

  • For best performance, use cached or striped DASD.

LAN Adapter Parameters

  • OS/2 Protocol Parameters (such as SizWorkBuf).

DEFAULTNET (Gateway Statement)

  • Specify packet size instead of using the default size.

Tuning for Small Packets

  • On X.25 or slow lines, delay acknowledgements and piggy-back on return. For example, MVS 3.1 GATEWAY DELAYACK

  • Note: For small partial packets, do not delay acknowledgements if the packet is less than the MTU.

  • Note: For Xwindows, use in setsockopt() TCP_NODELAY.

AIX Performance Considerations

  • For IBM RISC/6000 workstations you may want to change the packet size and window size because these variables have an impact on CPU cycles and can improve performance.

    • Issue the no -a command to view the current settings. You are required to be a root user on the RISC/6000 to make these changes.

    • Change the RISC/6000 packet size to 1500 bytes for Ethernet:

         ifconfig ethe down      
   ifconfig ether mtu 1500 
   netstat -in will display the current packet size

  • Change the RISC/6000 packet size to 4096 for Token Ring:

       ifconfig trl   down                     
   ifconfig trl   mtu 4096                         
   ifconfig trl   up

  • The recommended packet size for Token Ring and FDDI is 4096; Ethernet is 1500.

    Ensure that similar changes in TCP/IP profile on MVS are done to map the packet size. Use 1500 as the packet size on DEFAULTNET in the TCP/IP profile data set.

  • Using smit, set tcp_mssdflt to 4096 and recvnum and xmitnum to 64.

  • Use the following commands to change the RISC/6000 window size:

        no -o tcp-sendspace=32768 -o tcp-recvspace=32768
    no -o udp_sendspace=32768 o- udp_recvspace=32768

  • If you are using AIX Version 3.2.5 and RISC/6000 workstations as your TCP/IP client or server machine, you may want to install the IBM Authorized Program Analysis Report (APAR) #IX43314 and Problem Management Record (PMR) #4x948,322,000 to improve your FTP throughput for ASCII transfer and reduce host CPU cycles.

Adstar Distributed Storage Manager Performance Considerations

  • DATABUFFERPOOLSIZE x y in the TCPIP.PROFILE, where x indicates the number of buffers and y indicates the size of the buffer. The recommended size for the DATABUFFERPOOL is 32768. The default is 16384 if you have dynamic TCP control block PTF UN76873.

  • Packet size (GATEWAY) is 4096, and DEFAULTNET also needs to be 4096.

  • MVS dispatching priority plays a key role on performance, especially throughput. It is recommended that you keep TCP/IP and Virtual Telecommunications Access Method VTAM equivalent, and FTP and Adstar Distributed Storage Manager (ADSM) slightly lower than the TCP/IP task.

  • Region size(s) for TCP/IP, FTP, and ADSM servers. Define the region size for the TCP/IP to be OK or OM (assuming there are no storage constraints in the system).

  • Key parameters on the SP/2:

    Key Parameters

    File Size

    sb-max

    1310720

    thewall

    6000

    lowclust

    200

    mb_cl_hiwat

    1200

    tcp_sendspace

    32768

    tcp_recvspace

    32768

    udp_sendspace

    32768

    udp_recvspace

    32768

  • Install PTF IP20421 which superseded IP20334 and defined the parameters:

    • TCPWindowsize = 640

    • txnbyte = 25600

    • tcpnodelay = Y

    • tcp_mssdflt = 4096 (from 512)

    • recvnum and xmitnum = 64 (was already set)

    • MTU size on the SP2 to 4 KB

  • Run multiple separate transmissions in parallel from multiple SP/2 nodes using multiple Enterprise System Connection (ESCON) channels to one TCP/IP (MVS).

MVS TCP/IP Configuration Files

This section explains the important configuration/tuning files for MVS TCP/IP.

  • TCPIP.XXXXXXXX.TCPIP

    The MVS TCP/IP Profile contains buffer definitions, LAN controller definitions, server ports, home IP addresses, gateway statements, VTAM, Logical Units (LUs), for example.

  • TCPIP.TCPIP.DATA

    The MVS TCPIP DATA file contains host names, domain origin, nsinteraddr (name server), for example.

  • TCPIP.FTP.DATA

    For example, the MVS FTP DATA file contains LRECL, BLOCKSIZES, RECFM, CHKPTINT.

Related Information

Updated: Jan 18, 2008 Document ID: 12331