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

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Message-ID: <1318928605.2657.18.camel@edumazet-HP-Compaq-6005-Pro-SFF-PC>
Date:	Tue, 18 Oct 2011 11:03:25 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Giuseppe CAVALLARO <peppe.cavallaro@...com>
Cc:	netdev@...r.kernel.org, davem@...emloft.net,
	Deepak SIKRI <deepak.sikri@...com>
Subject: Re: [net-next 4/7] stmmac: allow mtu bigger than 1500 in case of
 normal desc (V3)

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 <deepak.sikri@...com>
> Signed-off-by: Giuseppe Cavallaro <peppe.cavallaro@...com>
> ---
>  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

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 ?

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);


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