Subject: Re: [net-next PATCH] e1000: add initial XDP support

From: John Fastabend <[email-masked]>
Date: Sun, 28 Aug 2016 22:36:59 -0700

On 16-08-28 08:56 AM, William Tu wrote:
> Hi,
> 
> Reading through the patch, I found some minor typos below.
> 
> On Sat, Aug 27, 2016 at 12:11 AM, John Fastabend
> <[email-masked]> wrote:
>> From: Alexei Starovoitov <[email-masked]>
>>
>> This patch adds initial support for XDP on e1000 driver. Note e1000
>> driver does not support page recycling in general which could be
>> added as a further improvement. However for XDP_DROP and XDP_XMIT
> 
> I think you mean XDP_PASS instead of XDP_XMIT?
> 

I really meant XDP_TX but see Or's note and next revision will have
XDP_DROP only here.

>> the xdp code paths will recycle pages.
>>
>> This patch includes the rcu_read_lock/rcu_read_unlock pair noted by
>> Brenden Blanco in another pending patch.
>>
>>   net/mlx4_en: protect ring->xdp_prog with rcu_read_lock
>>
>> CC: William Tu <[email-masked]>
>> Signed-off-by: Alexei Starovoitov <[email-masked]>
>> Signed-off-by: John Fastabend <[email-masked]>
>> ---
>>  drivers/net/ethernet/intel/e1000/e1000.h      |    1
>>  drivers/net/ethernet/intel/e1000/e1000_main.c |  168 ++++++++++++++++++++++++-
>>  2 files changed, 165 insertions(+), 4 deletions(-)
>>
>> +static void e1000_xmit_raw_frame(struct e1000_rx_buffer *rx_buffer_info,
>> +                                unsigned int len,
>> +                                struct net_device *netdev,
>> +                                struct e1000_adapter *adapter)
>> +{
>> +       struct netdev_queue *txq = netdev_get_tx_queue(netdev, 0);
>> +       struct e1000_hw *hw = &adapter->hw;
>> +       struct e1000_tx_ring *tx_ring;
>> +
>> +       if (len > E1000_MAX_DATA_PER_TXD)
>> +               return;
>> +
>> +       /* e1000 only support a single txq at the moment so the queue is being
>> +        * shared with stack. To support this requires locking to ensure the
>> +        * stack and XPD are not running at the same time. Devices would
>> +        * multiple queues should allocate a separate queue space.
>> +        */
> 
> XPD --> XDP
> Devices would --> with?

Yep typo.

> 
>> +       HARD_TX_LOCK(netdev, txq, smp_processor_id());
>> +
>> +       tx_ring = adapter->tx_ring;
>> +
>> +       if (E1000_DESC_UNUSED(tx_ring) < 2)
>> +               return;
>> +
>> +       e1000_tx_map_rxpage(tx_ring, rx_buffer_info, len);
>> +
>> +       e1000_tx_queue(adapter, tx_ring, 0/*tx_flags*/, 1);
>> +
>> +       writel(tx_ring->next_to_use, hw->hw_addr + tx_ring->tdt);
>> +       mmiowb();
>> +
>> +       HARD_TX_UNLOCK(netdev, txq);
>> +}
>> +
>>  #define NUM_REGS 38 /* 1 based count */
>>  static void e1000_regdump(struct e1000_adapter *adapter)
>>  {
>> @@ -4142,6 +4240,22 @@ static struct sk_buff *e1000_alloc_rx_skb(struct e1000_adapter *adapter,
>>         return skb;
>>  }
>>
>> +static inline int e1000_call_bpf(struct bpf_prog *prog, void *data,
>> +                                unsigned int length)
>> +{
>> +       struct xdp_buff xdp;
>> +       int ret;
>> +
>> +       xdp.data = data;
>> +       xdp.data_end = data + length;
>> +
>> +       rcu_read_lock();
>> +       ret = BPF_PROG_RUN(prog, (void *)&xdp);
>> +       rcu_read_unlock();
>> +
>> +       return ret;
>> +}
>> +
>>  /**
>>   * e1000_clean_jumbo_rx_irq - Send received data up the network stack; legacy
>>   * @adapter: board private structure
>> @@ -4160,12 +4274,15 @@ static bool e1000_clean_jumbo_rx_irq(struct e1000_adapter *adapter,
>>         struct pci_dev *pdev = adapter->pdev;
>>         struct e1000_rx_desc *rx_desc, *next_rxd;
>>         struct e1000_rx_buffer *buffer_info, *next_buffer;
>> +       struct bpf_prog *prog;
>>         u32 length;
>>         unsigned int i;
>>         int cleaned_count = 0;
>>         bool cleaned = false;
>>         unsigned int total_rx_bytes = 0, total_rx_packets = 0;
>>
>> +       rcu_read_lock(); /* rcu lock needed here to protect xdp programs */
>> +       prog = READ_ONCE(adapter->prog);
> 
> If having rcu_read_lock() here, do we still need another in e1000_call_bpf()?

nope good catch. Thanks for the review!