Subject: Re: [net-next 4/7] stmmac: allow mtu bigger than 1500 in case of normal desc (V3)

From: Giuseppe CAVALLARO <[email-masked]>
Date: Tue, 18 Oct 2011 11:26:10 +0200

Hello Eric,

On 10/18/2011 11:03 AM, Eric Dumazet wrote:
> Le mardi 18 octobre 2011 à 10:42 +0200, Giuseppe CAVALLARO a écrit :
>> This patch allows to set the mtu bigger than 1500
>> in case of normal descriptors.
>> This is helping some SPEAr customers.
>>
>> Signed-off-by: Deepak SIKRI <[email-masked]>
>> Signed-off-by: Giuseppe Cavallaro <[email-masked]>
>> ---
>>  drivers/net/ethernet/stmicro/stmmac/norm_desc.c   |    8 +++++++-
>>  drivers/net/ethernet/stmicro/stmmac/stmmac_main.c |    4 ++--
>>  2 files changed, 9 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/net/ethernet/stmicro/stmmac/norm_desc.c b/drivers/net/ethernet/stmicro/stmmac/norm_desc.c
>> index 029c2a2..e13226b 100644
>> --- a/drivers/net/ethernet/stmicro/stmmac/norm_desc.c
>> +++ b/drivers/net/ethernet/stmicro/stmmac/norm_desc.c
>> @@ -126,6 +126,7 @@ static void ndesc_init_rx_desc(struct dma_desc *p, unsigned int ring_size,
>>  	for (i = 0; i < ring_size; i++) {
>>  		p->des01.rx.own = 1;
>>  		p->des01.rx.buffer1_size = BUF_SIZE_2KiB - 1;
>> +		p->des01.rx.buffer2_size = BUF_SIZE_2KiB - 1;
>>  		if (i == ring_size - 1)
>>  			p->des01.rx.end_ring = 1;
>>  		if (disable_rx_ic)
>> @@ -183,7 +184,12 @@ static void ndesc_prepare_tx_desc(struct dma_desc *p, int is_fs, int len,
>>  				  int csum_flag)
>>  {
>>  	p->des01.tx.first_segment = is_fs;
>> -	p->des01.tx.buffer1_size = len;
>> +
>> +	if (unlikely(len > BUF_SIZE_2KiB)) {
>> +		p->des01.etx.buffer1_size = BUF_SIZE_2KiB - 1;
>> +		p->des01.etx.buffer2_size = len - p->des01.etx.buffer1_size;
>> +	} else
>> +		p->des01.tx.buffer1_size = len;
>>  }
>>  
>>  static void ndesc_clear_tx_ic(struct dma_desc *p)
>> diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
>> index d0af002..622b7ac 100644
>> --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
>> +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
>> @@ -1412,10 +1412,10 @@ static int stmmac_change_mtu(struct net_device *dev, int new_mtu)
>>  		return -EBUSY;
>>  	}
>>  
>> -	if (priv->plat->has_gmac)
>> +	if (priv->plat->enh_desc)
>>  		max_mtu = JUMBO_LEN;
>>  	else
>> -		max_mtu = ETH_DATA_LEN;
>> +		max_mtu = BUF_SIZE_4KiB;
>>  
>>  	if ((new_mtu < 46) || (new_mtu > max_mtu)) {
>>  		pr_err("%s: invalid MTU, max MTU is: %d\n", dev->name, max_mtu);
> 
> Problem using big mtu around 4096 bytes is you end allocating (4096
> +NET_SKB_PAD + NET_IP_ALIGN + sizeof(struct skb_shared_info) bytes ->
> 8192 bytes : order-1 pages

yes.

> 
> Maybe it would be better to limit your mtu to SKB_MAX_HEAD(NET_SKB_PAD),
> to have no more than one page per skb ?

ok! ;-)

> I would suggest changing netdev_alloc_skb_ip_align() done in
> init_dma_desc_rings() to use a variant allowing GFP_KERNEL allocations
> and allow your driver to load even in case of memory pressure.
> 
> diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> index c0ee6b6..8ec8057 100644
> --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> @@ -458,11 +458,12 @@ static void init_dma_desc_rings(struct net_device *dev)
>  	for (i = 0; i < rxsize; i++) {
>  		struct dma_desc *p = priv->dma_rx + i;
>  
> -		skb = netdev_alloc_skb_ip_align(dev, bfsize);
> +		skb = __netdev_alloc_skb(dev, bfsize + NET_IP_ALIGN, GFP_KERNEL);
>  		if (unlikely(skb == NULL)) {
>  			pr_err("%s: Rx init fails; skb is NULL\n", __func__);
>  			break;
>  		}
> +		skb_reserve(skb, NET_IP_ALIGN);
>  		priv->rx_skbuff[i] = skb;
>  		priv->rx_skbuff_dma[i] = dma_map_single(priv->device, skb->data,
>  						bfsize, DMA_FROM_DEVICE);
> 
> 
> 

Agree! I'm reviewing the patches and send all again.

Many thanks
Regards
Peppe