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Date:	Wed, 18 Jul 2007 18:32:48 -0400
From:	Jeff Garzik <jeff@...zik.org>
To:	Brian King <brking@...ux.vnet.ibm.com>
CC:	santil@...ux.vnet.ibm.com, rcjenn@...ux.vnet.ibm.com,
	netdev@...r.kernel.org, linuxppc-dev@...abs.org
Subject: Re: [PATCH 1/4] ibmveth: Enable TCP checksum offload

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 <brking@...ux.vnet.ibm.com>

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 <santil@...ibm.com>");
>  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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