> So if the CPU writes/reads to/from the same address, even atomically > (lock), there might be room for some inconsistency on the values? It > is not really atomic from the whole system point of view, just for the > HCA? If so, is there any possibility to make the whole operation > 'system-wide' atomic?
PCI does not have any capability for atomic operations until PCI Express 3.0 (not available in any real devices yet). So any current HCA performing atomic operations across a PCI bus will always have to do read-modify-write which leaves a window for the CPU to mess things up if it accesses the same location. You can work around this by creating a loopback connection (ie an RC connection from the local HCA to itself) and post atomic operations to that QP instead of accessing the memory directly with the CPU. - R. -- Roland Dreier <[email protected]> || For corporate legal information go to: http://www.cisco.com/web/about/doing_business/legal/cri/index.html -- To unsubscribe from this list: send the line "unsubscribe linux-rdma" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
