On Wed, 26 Jul 2006 10:28:00 -0700 "Ravinandan Arakali" <[EMAIL PROTECTED]> wrote:
> Hello, > Our current NIC does not provide the actual checksum value on receive path. > Hence we only claim NETIF_F_IP_CSUM instead of the more general > NETIF_F_HW_CSUM. > > To support this in a future adapter, we would like to know what exactly are > the requirements (on both Rx and Tx )to claim NETIF_F_HW_CSUM ? If you set NETIF_F_HW_CSUM, on transmit the adapter if ip_summed is set will be handed an unchecksummed frame with the offset to stuff the checksum at. Only difference between NETIF_F_HW_CSUM and NETIF_F_IP_CSUM is that IP_CSUM means the device can handle IPV4 only. NETIF_F_HW_CSUM has no impact on receive. The form of receive checksumming format is up to the device. It can either put one's complement in skb->csum and set ip_summed to CHECKSUM_HW or if device only reports checksum good then set CHECKSUM_UNNECESSARY. Several are a couple of subtleties to the receive processing: * Meaning of ip_summed changes from tx to rx path and that has to be handled in code that does forwarding like bridges. * If device only reports checksum okay vs bad. The packets marked bad might be another protocol, so should be passed up with CHECKSUM_NONE and let any checksum errors get detected in software. * Checksum HW on receive should work better since then IPV6 and nested protocols like VLAN's can be handled. > Following are some specific questions: > 1. On Tx, our adapter supports checksumming of TCP/UDP over IPv4 and IPv6. > This computation is TCP/UDP specific. Does the checksum calculation need to > be more generic ? Also, skbuff.h says that the checksum needs to be placed > at a specific location(skb->h.raw+skb->csum). I guess this means the adapter > needs to pass back the checksum to host driver after transmission. What > happens in case of TSO ? > 2. On Rx, is it suffficient if we place the L4 checksum in skb->csum ? What > about L3 checksum ? > The L3 checksum (IP) is always computed. Since the header is in CPU cache anyway it is faster that way. - To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
