Receive resources
Some adapters allow you to configure the number of resources used for receiving packets from the network. This might include the number of receive buffers (and even their size) or the number of DMA receive descriptors.
Some drivers have multiple receive buffer pools with buffers of different sizes that might need to be tuned for different workloads. Some drivers manage these resources internal to the driver and do not allow you to change them.
The receive resources might need to be increased to handle peak bursts on the network. The network interface device driver places incoming packets on a receive queue. If the receive descriptor list or ring is full, or no buffers are available, packets are dropped, resulting in the sender needing to retransmit. The receive descriptor queue is tunable using the SMIT tool or the chdev command (see Changing network parameters). The maximum queue size is specific to each type of communication adapter and can normally be viewed using the F4 or List key in the SMIT tool.
| Adapter Type | Feature Code | ODM attribute | Default value | Range |
|---|---|---|---|---|
| IBM® 10/100 Mbps Ethernet PCI Adapter | 2968 | rx_que_size rx_buf_pool_size |
256 384 |
16, 32 ,64, 128, 26 16-2048 |
| 10/100 Mbps Ethernet PCI Adapter II | 4962 | rx_desc_que_sz rxbuf_pool_sz |
512 1024 |
100-1024 512-2048 |
| Gigabit Ethernet PCI (SX or TX) | 2969, 2975 | rx_queue_size | 512 | 512 (fixed) |
| Gigabit Ethernet PCI-X (SX or TX) | 5700, 5701, 5706, 5707,5717, 5768, 5271, 5274, 5767, and 5281 | rxbuf_pool_sz rxdesc_que_sz |
2048 1024 |
512-16384,1 128-3840,128 |
| 10 Gigabit PCI-X (SR or LR) | 5718, 5719 | rxdesc_que_sz rxbuf_pool_sz |
1024 2048 |
128-1024, by 128 512-2048 |
| ATM 155 (MMF or UTP) | 4953, 4957 | rx_buf4k_min | x60 | x60-x200 (96-512) |
| ATM 622 (MMF) | 2946 | rx_buf4k_min rx_buf4k_max |
256 2 0 1 |
0-4096 0-14000 |
| FDDI | 2741, 2742, 2743 | RX_buffer_cnt | 42 | 1-512 |
- The ATM adapter's rx_buf4k_max attribute is the maximum number of buffers in the receive buffer pool. When the value is set to 0, the driver assigns a number based on the amount of memory on the system (rx_buf4k_max= thewall * 6 / 320, for example), but with upper limits of 9500 buffers for the ATM 155 adapter and 16360 buffers for the ATM 622 adapter. Buffers are released (down to rx_buf4k_min) when not needed.
- The ATM adapter's rx_buf4k_min attribute is the minimum number of free buffers in the pool. The driver tries to keep only this amount of free buffers in the pool. The pool can expand up to the rx_buf4k_max value.