Relationship between H/W ring and S/W ring

Hi

I`m reading the ixgbe code especially about H/W ring and S/W ring. Is the relationship between H/W ring and S/W ring one-to-one mapping? As far as I know, H/W ring size is determined in the code(hard coded) while S/W ring size is determined in port configuration time.
In the ixgbe_rx_alloc_bufs function, H/W ring header address and packet address indicate the DMA address of S/W ring's mbuf. I understand it means that the relationship between the H/W ring and S/W ring is one-to-one mapping. For example, if the size of H/W ring is greater than the size of S/W ring then some portion of H/W ring is unused. Is it correct?

Thanks

Quoted 12 lines

Hi

I`m reading the ixgbe code especially about H/W ring and S/W ring. Is the relationship between H/W ring and S/W ring one-to-one mapping? As far as I know, H/W ring size is determined in the code(hard coded) while S/W ring size is determined in port configuration time.
In the ixgbe_rx_alloc_bufs function, H/W ring header address and packet address indicate the DMA address of S/W ring's mbuf. I understand it means that the relationship between the H/W ring and S/W ring is one-to-one mapping. For example, if the size of H/W ring is greater than the size of S/W ring then some portion of H/W ring is unused. Is it correct?

Quoted 1 line

Thanks

Hi,

Yes, there is a 1:1 mapping between the hardware and software ring entries, and both are sized depending on the configuration parameters passed to the ring setup APIs. As you state, the HW ring contains the DMA addresses of the packet buffers, while the sw_ring contains the pointers to the original mbufs. The two rings are always kept in sync in the code.

/Bruce

Thanks Bruce.

I also agree with that the size of the S/W ring depends on the configuration parameters because the size of the S/W ring is /sizeof(struct igb_rx_entry)
* len/ in the ixgbe_dev_rx_queue_setup function. H/W ring is also allocated in the same function by using the ring_dma_zone_reserve function, and its size is RX_RING_SZ. I don't think the RX_RING_SZ is configurable but it is fixed value. Is there any other code configuring the size of H/W ring?

2014-10-30 오후 6:55에 Bruce Richardson 이(가) 쓴 글:

Quoted 20 lines · Gyumin

Quoted 12 lines

Hi

I`m reading the ixgbe code especially about H/W ring and S/W ring. Is the relationship between H/W ring and S/W ring one-to-one mapping? As far as I know, H/W ring size is determined in the code(hard coded) while S/W ring size is determined in port configuration time.
In the ixgbe_rx_alloc_bufs function, H/W ring header address and packet address indicate the DMA address of S/W ring's mbuf. I understand it means that the relationship between the H/W ring and S/W ring is one-to-one mapping. For example, if the size of H/W ring is greater than the size of S/W ring then some portion of H/W ring is unused. Is it correct?

Quoted 1 line

Thanks

Hi,

Yes, there is a 1:1 mapping between the hardware and software ring entries, and both are sized depending on the configuration parameters passed to the ring setup APIs. As you state, the HW ring contains the DMA addresses of the packet buffers, while the sw_ring contains the pointers to the original mbufs. The two rings are always kept in sync in the code.

/Bruce

Quoted 9 lines

Thanks Bruce.

I also agree with that the size of the S/W ring depends on the configuration parameters because the size of the S/W ring is /sizeof(struct igb_rx_entry)
* len/ in the ixgbe_dev_rx_queue_setup function. H/W ring is also allocated in the same function by using the ring_dma_zone_reserve function, and its size is RX_RING_SZ. I don't think the RX_RING_SZ is configurable but it is fixed value. Is there any other code configuring the size of H/W ring?

Indeed you are right, my mistake. The comment indicates that we always reserve the memory to be the maximum size so that we can resize the rings easier later on.
In terms of runtime usage, though, if you look a the RX functions, you can see that the two rings are always kept in sync. For example, looking at ixgbe_rxq_rearm in ixgbe_rxtx_vec.c, you will see that rxdp and rxep values both start at offset "rxq->rxrearm_start" at the top of the function, and that in the main rearm loop, both are incremented twice each iteration (rxep += 2 in the for statment itself, and two rxdp++'s are used in the last two lines of the loop body).

Regards,
/Bruce

Quoted 21 lines

2014-10-30 오후 6:55에 Bruce Richardson 이(가) 쓴 글:

Quoted 20 lines · Gyumin

Quoted 12 lines

Hi

I`m reading the ixgbe code especially about H/W ring and S/W ring. Is the relationship between H/W ring and S/W ring one-to-one mapping? As far as I know, H/W ring size is determined in the code(hard coded) while S/W ring size is determined in port configuration time.
In the ixgbe_rx_alloc_bufs function, H/W ring header address and packet address indicate the DMA address of S/W ring's mbuf. I understand it means that the relationship between the H/W ring and S/W ring is one-to-one mapping. For example, if the size of H/W ring is greater than the size of S/W ring then some portion of H/W ring is unused. Is it correct?

Quoted 1 line

Thanks

Hi,

Yes, there is a 1:1 mapping between the hardware and software ring entries, and both are sized depending on the configuration parameters passed to the ring setup APIs. As you state, the HW ring contains the DMA addresses of the packet buffers, while the sw_ring contains the pointers to the original mbufs. The two rings are always kept in sync in the code.

/Bruce