Brian King wrote:
This patchset enables TCP checksum offload support for IPV4
on ibmveth. This completely eliminates the generation and checking of
the checksum for packets that are completely virtual and never
touch a physical network. A simple TCP_STREAM netperf run on
a virtual network with maximum mtu set yielded a ~30% increase
in throughput. This feature is enabled by default on systems that
support it, but can be disabled with a module option.

Signed-off-by: Brian King <[EMAIL PROTECTED]>

this should be controllable purely via ethtool...


diff -puN drivers/net/ibmveth.c~ibmveth_csum_offload drivers/net/ibmveth.c
--- linux-2.6/drivers/net/ibmveth.c~ibmveth_csum_offload        2007-07-12 
08:27:47.000000000 -0500
+++ linux-2.6-bjking1/drivers/net/ibmveth.c     2007-07-12 09:35:55.000000000 
-0500
@@ -47,6 +47,8 @@
 #include <linux/mm.h>
 #include <linux/ethtool.h>
 #include <linux/proc_fs.h>
+#include <linux/in.h>
+#include <linux/ip.h>
 #include <asm/semaphore.h>
 #include <asm/hvcall.h>
 #include <asm/atomic.h>
@@ -103,12 +105,15 @@ static struct proc_dir_entry *ibmveth_pr
static const char ibmveth_driver_name[] = "ibmveth";
 static const char ibmveth_driver_string[] = "IBM i/pSeries Virtual Ethernet 
Driver";
+static unsigned int ibmveth_csum_offload = 1;
 #define ibmveth_driver_version "1.03"
MODULE_AUTHOR("Santiago Leon <[EMAIL PROTECTED]>");
 MODULE_DESCRIPTION("IBM i/pSeries Virtual Ethernet Driver");
 MODULE_LICENSE("GPL");
 MODULE_VERSION(ibmveth_driver_version);
+module_param_named(csum_offload, ibmveth_csum_offload, uint, 0);
+MODULE_PARM_DESC(csum_offload, "Checksum offload (0/1). Default: 1");
/* simple methods of getting data from the current rxq entry */
 static inline int ibmveth_rxq_pending_buffer(struct ibmveth_adapter *adapter)
@@ -131,6 +136,11 @@ static inline int ibmveth_rxq_frame_leng
        return (adapter->rx_queue.queue_addr[adapter->rx_queue.index].length);
 }
+static inline int ibmveth_rxq_csum_good(struct ibmveth_adapter *adapter)
+{
+       return 
(adapter->rx_queue.queue_addr[adapter->rx_queue.index].csum_good);
+}
+
 /* setup the initial settings for a buffer pool */
 static void ibmveth_init_buffer_pool(struct ibmveth_buff_pool *pool, u32 
pool_index, u32 pool_size, u32 buff_size, u32 pool_active)
 {
@@ -684,6 +694,24 @@ static int ibmveth_start_xmit(struct sk_
                                        desc[0].fields.length, DMA_TO_DEVICE);
        desc[0].fields.valid   = 1;
+ if (skb->ip_summed == CHECKSUM_PARTIAL &&
+           ip_hdr(skb)->protocol != IPPROTO_TCP && skb_checksum_help(skb)) {
+               ibmveth_error_printk("tx: failed to checksum packet\n");
+               tx_dropped++;
+               goto out;
+       }
+
+       if (skb->ip_summed == CHECKSUM_PARTIAL) {
+               unsigned char *buf = skb_transport_header(skb) + 
skb->csum_offset;
+
+               desc[0].fields.no_csum = 1;
+               desc[0].fields.csum_good = 1;
+
+               /* Need to zero out the checksum */
+               buf[0] = 0;
+               buf[1] = 0;
+       }
+
        if(dma_mapping_error(desc[0].fields.address)) {
                ibmveth_error_printk("tx: unable to map initial fragment\n");
                tx_map_failed++;
@@ -702,6 +730,10 @@ static int ibmveth_start_xmit(struct sk_
                                frag->size, DMA_TO_DEVICE);
                desc[curfrag+1].fields.length = frag->size;
                desc[curfrag+1].fields.valid  = 1;
+               if (skb->ip_summed == CHECKSUM_PARTIAL) {
+                       desc[curfrag+1].fields.no_csum = 1;
+                       desc[curfrag+1].fields.csum_good = 1;
+               }
if(dma_mapping_error(desc[curfrag+1].fields.address)) {
                        ibmveth_error_printk("tx: unable to map fragment %d\n", 
curfrag);
@@ -792,7 +824,11 @@ static int ibmveth_poll(struct net_devic
                        } else {
                                int length = ibmveth_rxq_frame_length(adapter);
                                int offset = ibmveth_rxq_frame_offset(adapter);
+                               int csum_good = ibmveth_rxq_csum_good(adapter);
+
                                skb = ibmveth_rxq_get_buffer(adapter);
+                               if (csum_good)
+                                       skb->ip_summed = CHECKSUM_UNNECESSARY;
ibmveth_rxq_harvest_buffer(adapter); @@ -962,8 +998,10 @@ static void ibmveth_poll_controller(stru
 static int __devinit ibmveth_probe(struct vio_dev *dev, const struct 
vio_device_id *id)
 {
        int rc, i;
+       long ret;
        struct net_device *netdev;
        struct ibmveth_adapter *adapter = NULL;
+       union ibmveth_illan_attributes set_attr, ret_attr;
unsigned char *mac_addr_p;
        unsigned int *mcastFilterSize_p;
@@ -1058,6 +1096,26 @@ static int __devinit ibmveth_probe(struc
ibmveth_debug_printk("registering netdev...\n"); + if (ibmveth_csum_offload) {
+               ret = h_illan_attributes(dev->unit_address, 0, 0, 
&ret_attr.desc);
+
+               if (ret == H_SUCCESS && !ret_attr.fields.active_trunk &&
+                   !ret_attr.fields.trunk_priority &&
+                   ret_attr.fields.csum_offload_padded_pkt_support) {
+                       set_attr.desc = 0;
+                       set_attr.fields.tcp_csum_offload_ipv4 = 1;
+
+                       ret = h_illan_attributes(dev->unit_address, 0, 
set_attr.desc,
+                                                &ret_attr.desc);
+
+                       if (ret == H_SUCCESS)
+                               netdev->features |= NETIF_F_IP_CSUM;
+                       else
+                               ret = h_illan_attributes(dev->unit_address, 
set_attr.desc,
+                                                        0, &ret_attr.desc);
+               }
+       }
+
        rc = register_netdev(netdev);
if(rc) {
diff -puN drivers/net/ibmveth.h~ibmveth_csum_offload drivers/net/ibmveth.h
--- linux-2.6/drivers/net/ibmveth.h~ibmveth_csum_offload        2007-07-12 
08:27:47.000000000 -0500
+++ linux-2.6-bjking1/drivers/net/ibmveth.h     2007-07-12 09:32:54.000000000 
-0500
@@ -67,6 +67,21 @@ static inline long h_send_logical_lan(un
        return rc;
 }
+static inline long h_illan_attributes(unsigned long unit_address,
+                                     unsigned long reset_mask, unsigned long 
set_mask,
+                                     unsigned long *ret_attributes)
+{
+       long rc;
+       unsigned long retbuf[PLPAR_HCALL_BUFSIZE];
+
+       rc = plpar_hcall(H_ILLAN_ATTRIBUTES, retbuf, unit_address,
+                        reset_mask, set_mask);
+
+       *ret_attributes = retbuf[0];
+
+       return rc;
+}
+
 #define h_multicast_ctrl(ua, cmd, mac) \
   plpar_hcall_norets(H_MULTICAST_CTRL, ua, cmd, mac)
@@ -144,7 +159,9 @@ struct ibmveth_adapter {
 struct ibmveth_buf_desc_fields {
     u32 valid : 1;
     u32 toggle : 1;
-    u32 reserved : 6;
+    u32 reserved : 4;
+    u32 no_csum : 1;
+    u32 csum_good : 1;
     u32 length : 24;
     u32 address;
 };
@@ -154,10 +171,30 @@ union ibmveth_buf_desc {
     struct ibmveth_buf_desc_fields fields;
 };
+struct ibmveth_illan_attributes_fields {
+       u32 reserved;
+       u32 reserved2 : 18;
+       u32 csum_offload_padded_pkt_support : 1;
+       u32 reserved3 : 1;
+       u32 trunk_priority : 4;
+       u32 reserved4 : 5;
+       u32 tcp_csum_offload_ipv6 : 1;
+       u32 tcp_csum_offload_ipv4 : 1;
+       u32 active_trunk : 1;
+};
+
+union ibmveth_illan_attributes {
+       u64 desc;
+       struct ibmveth_illan_attributes_fields fields;
+};
+
 struct ibmveth_rx_q_entry {
     u16 toggle : 1;
     u16 valid : 1;
-    u16 reserved : 14;
+    u16 reserved : 4;
+    u16 no_csum : 1;
+    u16 csum_good : 1;
+    u16 reserved2 : 8;
     u16 offset;

As a general rule, it would be nice to start moving away from bitfields in this driver

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