netdev - Re: [net-next PATCH v2 1/2] e1000: add initial XDP support

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Date:   Fri, 9 Sep 2016 16:33:10 -0700
From:   John Fastabend <john.fastabend@...il.com>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     bblanco@...mgrid.com, alexei.starovoitov@...il.com,
        jeffrey.t.kirsher@...el.com, brouer@...hat.com,
        davem@...emloft.net, xiyou.wangcong@...il.com,
        intel-wired-lan@...ts.osuosl.org, u9012063@...il.com,
        netdev@...r.kernel.org
Subject: Re: [net-next PATCH v2 1/2] e1000: add initial XDP support

On 16-09-09 03:04 PM, Eric Dumazet wrote:
> On Fri, 2016-09-09 at 14:29 -0700, John Fastabend wrote:
>> From: Alexei Starovoitov <ast@...com>
>>
> 
> 
> So it looks like e1000_xmit_raw_frame() can return early,
> say if there is no available descriptor.
> 
>> +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 XDP are not running at the same time. Devices with
>> +	 * multiple queues should allocate a separate queue space.
>> +	 */
>> +	HARD_TX_LOCK(netdev, txq, smp_processor_id());
>> +
>> +	tx_ring = adapter->tx_ring;
>> +
>> +	if (E1000_DESC_UNUSED(tx_ring) < 2) {
>> +		HARD_TX_UNLOCK(netdev, txq);
>> +		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 +4247,19 @@ static struct sk_buff *e1000_alloc_rx_skb(struct e1000_adapter *adapter,
>>  	return skb;
>>  }
>> +			act = e1000_call_bpf(prog, page_address(p), length);
>> +			switch (act) {
>> +			case XDP_PASS:
>> +				break;
>> +			case XDP_TX:
>> +				dma_sync_single_for_device(&pdev->dev,
>> +							   dma,
>> +							   length,
>> +							   DMA_TO_DEVICE);
>> +				e1000_xmit_raw_frame(buffer_info, length,
>> +						     netdev, adapter);
>> +				buffer_info->rxbuf.page = NULL;
> 
> 
> So I am trying to understand how pages are not leaked ?
> 
> 

Pages are being leaked thanks! v3 coming soon.