Evgeniy Polyakov wrote:
On Fri, Sep 22, 2006 at 10:33:48PM -0700, Andrew Morton ([email protected]) wrote:
The NET_IP_ALIGN existed not just for fun :) There are ramifications
for removing it.
It's still there, isn't it?
For the 9k MTU case, for example, we end up allocating 16384 byte skbs
instead of 32786 kbytes ones.
This patch will not help - netdev_alloc_skb() adds additional
NET_SKB_PAD and then alloc_skb() adds sizeof(struct skb_shared_info).
And even if you acconut for them in adapter->rx_buf_len, chip still can
overwrite that area (in the thread mentioned in this e-mail thread
before I posted such patch and received a dump of sizes chip receives -
there were a lot of _different_ ones which were too close to the limit).
I just did the math on it and it does not compute as I wanted too, we're
basically flowing to the next larger buffersize 2 mtu bytes earlier, undoing
any benefit completely.
There is not much that can fix this issue since the hardware will always
receive in 2-order buffers and dma that back in its entirity, so we must always
claim size for NET_IP_ALIGN and NET_SKB_PAD after the 2-order bufsz. For the
9kb mtu case (16kb hw bufsz), we're stuck with 32kb slab allocations. bummer.
Andrew, please drop this patch.
Auke
diff -puN drivers/net/e1000/e1000_main.c~e1000-account-for-net_ip_align-when-calculating-bufsiz drivers/net/e1000/e1000_main.c
--- a/drivers/net/e1000/e1000_main.c~e1000-account-for-net_ip_align-when-calculating-bufsiz
+++ a/drivers/net/e1000/e1000_main.c
@@ -1101,7 +1101,7 @@ e1000_sw_init(struct e1000_adapter *adap
pci_read_config_word(pdev, PCI_COMMAND, &hw->pci_cmd_word);
- adapter->rx_buffer_len = MAXIMUM_ETHERNET_VLAN_SIZE;
+ adapter->rx_buffer_len = MAXIMUM_ETHERNET_VLAN_SIZE + NET_IP_ALIGN;
adapter->rx_ps_bsize0 = E1000_RXBUFFER_128;
hw->max_frame_size = netdev->mtu +
ENET_HEADER_SIZE + ETHERNET_FCS_SIZE;
@@ -3163,26 +3163,27 @@ e1000_change_mtu(struct net_device *netd
* larger slab size
* i.e. RXBUFFER_2048 --> size-4096 slab */
- if (max_frame <= E1000_RXBUFFER_256)
+ if (max_frame + NET_IP_ALIGN <= E1000_RXBUFFER_256)
adapter->rx_buffer_len = E1000_RXBUFFER_256;
- else if (max_frame <= E1000_RXBUFFER_512)
+ else if (max_frame + NET_IP_ALIGN <= E1000_RXBUFFER_512)
adapter->rx_buffer_len = E1000_RXBUFFER_512;
- else if (max_frame <= E1000_RXBUFFER_1024)
+ else if (max_frame + NET_IP_ALIGN <= E1000_RXBUFFER_1024)
adapter->rx_buffer_len = E1000_RXBUFFER_1024;
- else if (max_frame <= E1000_RXBUFFER_2048)
+ else if (max_frame + NET_IP_ALIGN <= E1000_RXBUFFER_2048)
adapter->rx_buffer_len = E1000_RXBUFFER_2048;
- else if (max_frame <= E1000_RXBUFFER_4096)
+ else if (max_frame + NET_IP_ALIGN <= E1000_RXBUFFER_4096)
adapter->rx_buffer_len = E1000_RXBUFFER_4096;
- else if (max_frame <= E1000_RXBUFFER_8192)
+ else if (max_frame + NET_IP_ALIGN <= E1000_RXBUFFER_8192)
adapter->rx_buffer_len = E1000_RXBUFFER_8192;
- else if (max_frame <= E1000_RXBUFFER_16384)
+ else
adapter->rx_buffer_len = E1000_RXBUFFER_16384;
/* adjust allocation if LPE protects us, and we aren't using SBP */
if (!adapter->hw.tbi_compatibility_on &&
((max_frame == MAXIMUM_ETHERNET_FRAME_SIZE) ||
(max_frame == MAXIMUM_ETHERNET_VLAN_SIZE)))
- adapter->rx_buffer_len = MAXIMUM_ETHERNET_VLAN_SIZE;
+ adapter->rx_buffer_len = MAXIMUM_ETHERNET_VLAN_SIZE +
+ NET_IP_ALIGN;
netdev->mtu = new_mtu;
@@ -4002,7 +4003,8 @@ e1000_alloc_rx_buffers(struct e1000_adap
struct e1000_buffer *buffer_info;
struct sk_buff *skb;
unsigned int i;
- unsigned int bufsz = adapter->rx_buffer_len + NET_IP_ALIGN;
+ /* we have already accounted for NET_IP_ALIGN */
+ unsigned int bufsz = adapter->rx_buffer_len;
i = rx_ring->next_to_use;
buffer_info = &rx_ring->buffer_info[i];
_
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