ImprovingNetwork Performance 27
4
Improving Performance
The following section describes how to modify the user-configurable network
parameters. Toobtain optimum network performance, you may need to tune
these parameters, depending on your network configuration and the type of
network traffic.

Changing the High and Low WaterMarks

The maximum rate at which data is transferred between user space and kernel
space by applications that use STREAMS is controlled by the high water marks.
These parameters define the maximum amount of data that can be queued for
transmission to the TCP or UDP STREAMS modules. There are independent
send and receive high water marks for TCP and UDP applications.
When the number of bytes queued exceeds the high water mark, transmission
is halted temporarily the backlog can be cleared. The low water mark specifies
the level to which the queue must drop before transmission is restarted.

▼To Tunethe High Water Mark

Assign consistent values for the transmit and receive high water marks. The
default value (8192) assigned to these parameters is optimized for transmitting
across Ethernet connections. For applications running over FDDI, the high
water marks should be set to 32 Kbytes. Use ndd(1M) to change the TCP and
UDP high water marks:
1. Log in as root or become superuser.
2. Use ndd —get (the default) to check the current value of the TCP high
water marks (tcp_xmit_hiwat and tcp_recv_hiwat).
#ndd /dev/tcp tcp_xmit_hiwat
8192
#ndd /dev/tcp tcp_recv_hiwat
8192