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

Neil Horman
2013-07-28T23:38:40Z

On Sun, Jul 28, 2013 at 04:20:54PM -0700, Eric Dumazet wrote:
> 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");
>
>
>
HA! I was 99% right on my first patch! :) Luis, Can you test this patch out
and confirm that it fixes the issue.
Neil