User`s guide

Chapter XI. UDP Segmentation Offload and Pacing

Chelsio T5/T4 Unified Wire For Linux Page 179

4.2. Configuring UDP Pacing

Now that the application has been modified to associate the application’s UDP socket to a

particular UDP traffic class, the pacing of that socket’s traffic can be set using the cxgbtool

utility. The command and its parameters are explained below:

[root@host]# cxgbtool <ethX> sched-class params type packet level cl-rl

mode flow rate-unit bits rate-mode absolute channel <Channel No.> class

<scheduler-class-index> max-rate <maximum-rate> pkt-size <Packet size>

Here,

 ethX is the Chelsio interface

 Channel No. is the port on which data is flowing (0-3)

 scheduler-class-index is the UDP traffic class (0-14) set in the SOL_SCHEDCLASS socket

option in the application in section 4.1.

 maximum-rate is the bit rate (Kbps) for this UDP stream. This value should be in the range

of 50 Kbps to 50 Mbps.

 Packet size is the UDP packet payload size in bytes; it should be equal to the value set in

the SO_FRAMESIZE socket option in the application in section 4.1.

Example:

The user wants to transfer UDP data on port 0 of the adapter using the USO engine. The

application has been modified as shown in section 4.1. In order to set a bit rate of 10Mbps for

traffic class 1 with payload size of 1316 on port 0, the following invocation of cxgbtool is used:

[root@host]# cxgbtool ethX sched-class params type packet level cl-rl

mode flow rate-unit bits rate-mode absolute channel 0 class 1 max-rate

10000 pkt-size 1316

To get an accurate bit rate per class, data sent by the application to the

sockets should be a multiple of the value set for the “pkt-size” parameter.

In above example, IO size sent by application should be a multiple of 1316.

Linux Unified Wire currently supports 10240 offload UDP connections. If the

application needs to establish more than 10240 UDP connections, it can

check the return code of ENOSPC from a send() or sendto() call and close

this socket and open a new one that uses the kernel UDP stack.

Note