Re: [net PATCH] atl1c: Fix misuse of netdev_alloc_skb in refilling rx ring

Eric Dumazet
2013-07-28T23:20:56Z

On Sun, 2013-07-28 at 16:01 -0700, Eric Dumazet wrote:
> On Sun, 2013-07-28 at 21:22 +0100, Ben Hutchings wrote:
>
> >
> > Since we know lengths > 4K work, perhaps it would be worth testing with
> > the fragment cache size reduced to 16K? The driver would never
> > previously have used RX buffers crossing 16K boundaries, except if SLOB
> > was used (and that's an unlikely combination).
>
> Sure, please note the following maths :
>
> NET_SKB_PAD + 1536 + sizeof(struct skb_shared_info) = 1920
>
> 16384/1920 = 8
>
> 32768/1920 = 17
>
> I don't think atl1c is used in any critical host (given it doesn't even
> provide RX checksums and GRO ...), so I will provide a patch doing mere
> page allocations.
>

Oh well, look at code around line 2530

* The atl1c chip can DMA to 64-bit addresses, but it uses a single
* shared register for the high 32 bits, so only a single, aligned,
* 4 GB physical address range can be used at a time.
*
* Supporting 64-bit DMA on this hardware is more trouble than it's
* worth. It is far easier to limit to 32-bit DMA than update
* various kernel subsystems to support the mechanics required by a
* fixed-high-32-bit system.
*/
if ((pci_set_dma_mask(pdev, DMA_BIT_MASK(32)) != 0) ||
(pci_set_consistent_dma_mask(pdev, DMA_BIT_MASK(32)) != 0)) {
dev_err(&pdev->dev, "No usable DMA configuration,aborting\n");
goto err_dma;
}

It looks like we have a winner !

This $@!? really needs DMA32 allocations.

Currently only tested on TX patch, it needs same care on RX

diff --git a/drivers/net/ethernet/atheros/atl1c/atl1c_main.c b/drivers/net/ethernet/atheros/atl1c/atl1c_main.c
index 786a874..e2ee962 100644
--- a/drivers/net/ethernet/atheros/atl1c/atl1c_main.c
+++ b/drivers/net/ethernet/atheros/atl1c/atl1c_main.c
@@ -1660,7 +1660,8 @@ static int atl1c_alloc_rx_buffer(struct atl1c_adapter *adapter)
while (next_info->flags & ATL1C_BUFFER_FREE) {
rfd_desc = ATL1C_RFD_DESC(rfd_ring, rfd_next_to_use);

- skb = netdev_alloc_skb(adapter->netdev, adapter->rx_buffer_len);
+ skb = __netdev_alloc_skb(adapter->netdev, adapter->rx_buffer_len,
+ GFP_ATOMIC | GFP_DMA32);
if (unlikely(!skb)) {
if (netif_msg_rx_err(adapter))
dev_warn(&pdev->dev, "alloc rx buffer failed\n");