UDP, TCP/IP, and mbuf Tuning Parameters Summary

AIX Versions 3.2 and 4 Performance Tuning Guide

The following paragraphs summarize the attributes and tuning techniques for each of the communications tuning parameters.

Purpose:	Provide an absolute upper bound on the amount of real memory that can be used by the communication subsystem.
Values:	AIX 4.2.1 and earlier: Default: 1/8 of real memory. Range: up to 1/2 of real memory or 65536 (64 megabytes), whichever is smaller. AIX 4.3.0: Default: 1/8 of real memory. Range: up to 1/2 of real memory or 131072 (128 megabytes), whichever is smaller. AIX 4.3.1: Default: 1/2 of real memory. Range: up to 1/2 of real memory or 131072 (128 megabytes), whichever is smaller.
Display:	no -a or no -o thewall
Change:	no -o thewall=newvalue newvalue is in KB, not bytes Change takes effect immediately for new connections. Change is effective until the next system boot.
Diagnosis:	None.
Tuning:	Increase size, preferably to multiple of 4(KB).
Refer to:	"mbuf Pool Performance Tuning" .

Purpose:	In AIX Version 4.3.1 or later, provide a way to prevent new sockets from being created when almost all the network memory is in use.
Values:	Default: 85% of thewall. Range: 1-100
Display:	no -a or no -o sockthresh
Change:	no -o sockthresh=newvalue newvalue is a percentage of thewall. Change takes effect immediately. Change is effective until the next system boot. Note: Change will fail if the user attempts to set a new value that is less than the amount of memory currently in use.
Diagnosis:	None.
Tuning:	Decrease percentage.
Refer to:	"Socket Layer" .

Purpose:	Provide an absolute upper bound on the size of TCP and UDP socket buffers. Limits setsockopt(), udp_sendspace, udp_recvspace, tcp_sendspace, and tcp_recvspace.
Values:	Default: 65536 Range: N/A
Display:	no -a or no -o sb_max
Change:	no -o sb_max=newvalue Change takes effect immediately for new connections. Change is effective until the next system boot.
Diagnosis:	None.
Tuning:	Increase size, preferably to multiple of 4096. Should be about twice the largest socket buffer limit.
Refer to:	"Socket Layer".

Purpose:	Value of 1 indicates that tcp_sendspace and tcp_recvspace can exceed 64KB.
Values:	Default: 0 Range: 0 or 1
Display:	no -a or no -o rfc1323
Change:	no -o rfc1323=newvalue Change takes effect immediately. Change is effective until the next system boot.
Diagnosis:	None.
Tuning:	Change before attempting to set tcp_sendspace and tcp_recvspace to more than 64KB.
Refer to:	"TCP Layer".

Purpose:	Provide the default value for the size of the UDP socket send buffer.
Values:	Default: 9216 Range: 0 to 65536 Must be less than or equal to sb_max.
Display:	no -a or no -o udp_sendspace
Change:	no -o udp_sendspace=newvalue Change takes effect immediately for new connections. Change is effective until the next system boot.
Diagnosis:	None.
Tuning:	Increase size, preferably to multiple of 4096.
Refer to:	"Socket Layer".

Purpose:	Provide the default value of the size of the UDP socket receive buffer.
Values:	Default: 41600 Range: N/A Must be less than or equal to sb_max.
Display:	no -a or no -o udp_recvspace
Change:	no -o udp_recvspace=newvalue Change takes effect immediately for new connections. Change is effective until the next system boot.
Diagnosis:	Nonzero n in netstat -s report of udp: n socket buffer overflows
Tuning:	Increase size, preferably to multiple of 4096.
Refer to:	"Socket Layer".

Purpose:	Provide the default value of the size of the TCP socket send buffer.
Values:	Default: 16384 Range: 0 to 64KB if rfc1323=0, Range: 0 to 4GB if rfc1323=1. Must be less than or equal to sb_max. Should be equal to tcp_recvspace and uniform on all frequently accessed AIX systems.
Display:	no -a or no -o tcp_sendspace
Change:	no -o tcp_sendspace=newvalue Change takes effect immediately for new connections. Change is effective until the next system boot.
Diagnosis:	Poor throughput.
Tuning:	Increase size, preferably to multiple of 4096.
Refer to:	"Socket Layer".

Purpose:	Provide the default value of the size of the TCP socket receive buffer.
Values:	Default: 16384 Range: 0 to 64KB if rfc1323=0, Range: 0 to 4GB if rfc1323=1. Must be less than or equal to sb_max. Should be equal to tcp_sendspace and uniform on all frequently accessed AIX systems.
Display:	no -a or no -o tcp_recvspace
Change:	no -o tcp_recvspace=newvalue Change takes effect immediately for new connections. Change is effective until the next system boot.
Diagnosis:	Poor throughput.
Tuning:	Increase size, preferably to multiple of 4096.
Refer to:	"Socket Layer".

Purpose:	Specify the maximum number of entries on the IP input queue.
Values:	Default: 50 Range: N/A
Display:	no -a or no -o ipqmaxlen
Change:	no -o ipqmaxlen=newvalue Change takes effect immediately. Change is effective until the next system boot.
Diagnosis:	Use crash to access IP input queue overflow counter.
Tuning:	Increase size.
Refer to:	"IP Protocol Performance Tuning Recommendations".

Purpose:	Specifies the maximum number of send buffers that can be queued up for the device.
Values:	Default: 30 Range: 20 to 150
Display:	lsattr -E -l tok0 -a xmt_que_size
Change:	ifconfig tr0 detach chdev -I tok0 -a xmt_que_size=newvalue ifconfig tr0 hostname up Change is effective across system boots.
Diagnosis:	netstat -i `Oerr > 0`
Tuning:	Increase size. Should be set to 150 as a matter of course on network-oriented systems, especially servers.
Refer to:	"LAN Adapters and Device Drivers".

Purpose:	(Tunable only in AIX Version 3.) Specifies the maximum number of receive buffers that can be queued up for the interface.
Values:	Default: 30 Range: 20 to 150
Display:	lsattr -E -l tokn -a rec_que_size
Change:	ifconfig tr0 detach chdev -I tokn -a rec_que_size=newvalue ifconfig tr0 hostname up Change is effective across system boots.
Diagnosis:	None.
Tuning:	Increase size. Should be set to 150 as a matter of course on network-oriented systems, especially servers.
Refer to:	"LAN Adapters and Device Drivers".

Purpose:	Limits the size of packets that are transmitted on the network.
Values:	trn (4Mb): Default: 1492, Range: 60 to 3900 trn (16Mb): Default: 1492, Range: 60 to 17960 enn: Default: 1500, Range: 60 to 1500 fin: Default: 4352, Range: 60 to 4352 hin: Default: 65536, Range: 60 to 65536 son: Default: 61428, Range: 60 to 61428 lon: Default: 1500 (AIX Version 3.2.5), 16896 (AIX Version 4), Range: 60 to 65536
Display:	lsattr -E -l trn
Change:	chdev -l trn -a mtu=NewValue Cannot be changed while the interface is in use. Because all systems on a LAN must have the same MTU, they must all change simultaneously. Change is effective across boots.
Diagnosis:	Packet fragmentation stats
Tuning:	Increase MTU size for the Token-Ring interfaces: trn (4Mb): 4056 trn (16Mb): 8500 For the loopback interface lon in Version 3.2.5, increase to 16896 For other interfaces, the default should be kept.
Refer to:	"LAN Adapters and Device Drivers".

The crash command, ifconfig command, lsattr command, netstat command, no command.

The setsockopt subroutine.