On Thu, Jul 30, 2015 at 11:46:36PM +0300, Yuval Shaia wrote: > On Thu, Jul 30, 2015 at 11:15:38AM -0600, Jason Gunthorpe wrote: > > On Thu, Jul 30, 2015 at 11:51:12AM -0400, Doug Ledford wrote: > > > > > In its current state, I have my doubts about this patch. However, it > > > seems to me that this should be relatively easy to fix in such a way > > > that you get 90%+ of the performance benefit, and can turn it on by > > > default, and we don't cause any problems. > > > > The best way to implement this is to leverage all the checksum > > offload work people did for virtualization. > > > > Forward the checksum offload status through the RC connection and > > recover it on the other side. > The current approach is to utilize IPoIB's private-data to exchange this > information. You need private-data exchange to negotiate the feature. The feature should be a per-packet csum status header. When sending a skb that is already fully csumed the receiver sets CHECKSUM_UNNECESSARY. When sending a skb that has CHECKSUM_PARTIAL then the receiver needs to call skb_partial_csum_set. Look at how something like VIRTIO_NET_HDR_F_NEEDS_CSUM works and copy that scheme. DO NOT EVER set CHECKSUM_UNNECESSARY on packets that do not have valid csums - that breaks the net stack. Yes, you need to add a header to all packets to support this scheme, that is what the private-data negotiation is for. While you are at it, I'd make room for something like VIRTIO_NET_HDR_GSO_* in the RC protocol too. Implementing GSO forwarding is probably another big performance win. Jason -- To unsubscribe from this list: send the line "unsubscribe linux-rdma" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
