Re: [PATCH net-next] net: lantiq_xrx200: use skb cache

Aleksander Bajkowski
2022-07-13T20:38:42Z

Hi Eric,

On 7/13/22 14:50, Eric Dumazet wrote:
> On Tue, Jul 12, 2022 at 8:15 PM Aleksander Jan Bajkowski <olek2@wp.pl> wrote:
>>
>> napi_build_skb() reuses NAPI skbuff_head cache in order to save some
>> cycles on freeing/allocating skbuff_heads on every new Rx or completed
>> Tx.
>> Use napi_consume_skb() to feed the cache with skbuff_heads of completed
>> Tx. The budget parameter is added to indicate NAPI context, as a value
>> of zero can be passed in the case of netpoll.
>>
>> NAT performance results on BT Home Hub 5A (kernel 5.15.45, mtu 1500):
>>
>> Fast path (Software Flow Offload):
>> Up Down
>> Before 702.4 719.3
>> After 707.3 739.9
>>
>> Slow path:
>> Up Down
>> Before 91.8 184.1
>> After 92.0 185.7
>>
>> Signed-off-by: Aleksander Jan Bajkowski <olek2@wp.pl>
>> ---
>> drivers/net/ethernet/lantiq_xrx200.c | 4 ++--
>> 1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/net/ethernet/lantiq_xrx200.c b/drivers/net/ethernet/lantiq_xrx200.c
>> index 5edb68a8aab1..83e07404803f 100644
>> --- a/drivers/net/ethernet/lantiq_xrx200.c
>> +++ b/drivers/net/ethernet/lantiq_xrx200.c
>> @@ -238,7 +238,7 @@ static int xrx200_hw_receive(struct xrx200_chan *ch)
>> return ret;
>> }
>>
>> - skb = build_skb(buf, priv->rx_skb_size);
>> + skb = napi_build_skb(buf, priv->rx_skb_size);
>
> If you are changing this code path, what about adding proper error recovery ?
>
> skb can be NULL at this point :/
>

Good catch. I will try to test the fix on the device tomorrow and send the patch.

>> skb_reserve(skb, NET_SKB_PAD);
>> skb_put(skb, len);
>>
>> @@ -321,7 +321,7 @@ static int xrx200_tx_housekeeping(struct napi_struct *napi, int budget)
>> pkts++;
>> bytes += skb->len;
>> ch->skb[ch->tx_free] = NULL;
>> - consume_skb(skb);
>> + napi_consume_skb(skb, budget);
>> memset(&ch->dma.desc_base[ch->tx_free], 0,
>> sizeof(struct ltq_dma_desc));
>> ch->tx_free++;
>> --
>> 2.30.2
>>

Best regards,
Aleksander