[openib-general] [PATCH 3/7] IB/ipoib - Use the new verbs DMA mapping functions

[Michael S. Tsirkin]

Quoting r. Ralph Campbell <ralph.campbell at qlogic.com>:
> diff -r f37bd0e41fec drivers/infiniband/ulp/ipoib/ipoib_ib.c
> --- a/drivers/infiniband/ulp/ipoib/ipoib_ib.c	Thu Oct 26 21:44:41 2006 +0700
> +++ b/drivers/infiniband/ulp/ipoib/ipoib_ib.c	Thu Oct 26 12:37:09 2006 -0800
> @@ -109,9 +109,8 @@ static int ipoib_ib_post_receive(struct 
>  	ret = ib_post_recv(priv->qp, &param, &bad_wr);
>  	if (unlikely(ret)) {
>  		ipoib_warn(priv, "receive failed for buf %d (%d)\n", id, ret);
> -		dma_unmap_single(priv->ca->dma_device,
> -				 priv->rx_ring[id].mapping,
> -				 IPOIB_BUF_SIZE, DMA_FROM_DEVICE);
> +		ib_dma_unmap_single(priv->ca, priv->rx_ring[id].mapping,
> +				    IPOIB_BUF_SIZE, DMA_FROM_DEVICE);
>  		dev_kfree_skb_any(priv->rx_ring[id].skb);
>  		priv->rx_ring[id].skb = NULL;
>  	}

Hmm, since ib_dma_unmap_single calls a function through a pointer,
this seems to introduce overhead on data path operations in ipoib.
For apps like ipoib always working with low memory, I think it is important to avoid this
overhead of extra indirect function calls at least on systems without IO MMU -
where e.g. dma_unmap_single is empty.
This probably means you need some of architecture-dependent code,
but should be possible - look at how dma API is implemented for an example.
And this applies to all ULPs on systems without high memory.

-- 
MST