rx ring buffer sizes cannot be modified with ethtool on be2net network interfaces

Solution Verified - Updated

Environment

  • Red Hat Enterprise Linux 5
  • Red Hat Enterprise Linux 6
  • be2net network interface driver

Issue

When attempting to modify the receive (rx) ring buffer size on a be2net network interface with the ethtool utility, an error message is displayed

> [root@server ~]\# ethtool -G eth0 rx 512  
> Cannot set device ring parameters: Operation not supported

Is it not possible to modify the rx ring buffer size with be2net network interfaces?

Resolution

There is no way to set the ring size when using be2net driver.

Root Cause

The BE2/3 NIC has fixed queues lengths, 1024 for each RX queue and 2048 for TX queue.

For RHEL 5 up to 5.10 and RHEL 6 up to 6.2, an output from ethtool -g <ethX> says how many entries in the RX queue is available for adaptor and how many entries in the TX queue were submitted (# of pending output packets/frags).

Example:

[root@bl460c-g7-03 ~]# ethtool -g eth4
Ring parameters for eth4:
Pre-set maximums:
RX:             1024
RX Mini:        0
RX Jumbo:       0
TX:             2048
Current hardware settings:
RX:             972
RX Mini:        0
RX Jumbo:       0
TX:             4
  • 972 of 1024 entries in the RX queue are available for incoming packets (52 to be refilled)
  • 4 pending outgoing packets are in the TX queue and waiting.

For RHEL 5.10, 6.3 and laters, it will only show the maximum values. It does will not show anymore the in-use values.

Diagnostic Steps

Check current ring params with the following script:

> [root@server ~]\# for i in \`seq 1 3\`; do date; ethtool -g eth0 |grep -A1 Current ; sleep 1 ; done  
>   
> Wed May 4 15:52:55 CDT 2011  
> Current hardware settings:  
> RX: 972  
>   
>   
> Wed May 4 15:52:56 CDT 2011  
> Current hardware settings:  
> RX:965  
>   
>   
> Wed May 4 15:52:57 CDT 2011  
> Current hardware settings:  
> RX: 962

You will notice that it changes by itself. That's because it actually has a different meaning.

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