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Date:   Wed, 13 Jul 2022 22:38:37 +0200
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Subject: Re: [PATCH net-next] net: lantiq_xrx200: use skb cache
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To:     Eric Dumazet <edumazet@google.com>
Cc:     hauke@hauke-m.de, David Miller <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>,
        netdev <netdev@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>
References: <20220712181456.3398-1-olek2@wp.pl>
 <CANn89iLbFYaV9MhYMHAzZOKM=ZKaAPOAuuXec_t9G5s4ypnY6A@mail.gmail.com>
From:   Aleksander Bajkowski <olek2@wp.pl>
In-Reply-To: <CANn89iLbFYaV9MhYMHAzZOKM=ZKaAPOAuuXec_t9G5s4ypnY6A@mail.gmail.com>
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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