Technical data

Tuning Techniques
2.1 Subsystem Attributes
2.1.4 Modifying Kernel Subsystems
Most resources used by the network subsystem are allocated and adjusted
dynamically. However, you can make some adjustments to improve performance.
Table 2–1 summarizes the adjustments you can make, lists performance benefits
and the adjustments that will achieve them, along with the tradeoffs (where
applicable) associated with each adjustment.
Table 2–1 Network Tuning Guidelines
Performance Benefit Tuning Adjustment Tradeoff
Reduce the number of dropped incoming
connection requests.
Increase the maximum number
of pending TCP connections
(Section 2.1.5.1).
Consumes memory resources.
Allow each server socket to handle more
SYN packets simultaneously.
Increase the minimum number
of pending TCP connections
(Section 2.1.5.2).
Consumes memory resources.
Allow for a larger socket buffer. Increase the maximum socket buffer size
(Section 2.1.5.3).
Consumes memory. If you have
a large number of sockets,
memory consumption could be
of concern.
Improve the TCP control block lookup
rate and increase the raw connection
rate.
Increase the size of the hash table that
the kernel uses to look up TCP control
blocks (Section 2.1.6.1).
Slightly increases the amount
of pooled memory.
Reduce hash table lock contention for
SMP systems.
Increase the number of TCP hash tables
(Section 2.1.6.2).
Slightly increases the amount
of pooled memory.
Improve performance on systems that
use large numbers of interface alias.
Increase the size of the kernel interface
alias table (Section 2.1.6.3).
None.
Allow partial connections to time out
sooner, preventing the socket listen
queue from filling up with SYN packets.
Increase the TCP partial connection
timeout rate (Section 2.1.6.4).
Setting the
tcp_keepinit
value too low can cause
connections to be broken
prematurely.
Prevent premature retransmissions and
decrease congestion.
Reduce the TCP retransmission rate
(Section 2.1.6.5).
A long retransmit time
is not appropriate for all
configurations.
Clean up sockets that do not exit cleanly
when the
keepalive interval expires.
Enable TCP keepalive functionality
(Section 2.1.6.6).
None.
Free connection resources sooner. Make the TCP connection context time
out more quickly at the end of the
connection (Section 2.1.6.7).
Reducing the timeout limit
increases the potential for data
corruption; use caution if you
make this adjustment.
Provide TCP and UDP applications with
a specific range of ports.
Modify the range of outgoing connection
ports (Section 2.1.6.9).
None.
Improve the efficiency of servers that
handle remote traffic from many clients.
Disable the use of a PMTU
(Section 2.1.6.10).
May reduce server efficiency for
LAN traffic.
Allow large socket buffer sizes. Increase the maximum size of a socket
buffer (Section 2.1.5.3).
Consumes memory resources.
Improve handling of a large number of
BG devices.
Enable fast device creation and deletion
(Section 2.2.4).
Consumes memory resources.
The following sections describe in detail how to modify socket and inet
subsystem attributes.
Tuning Techniques 2–7