From mboxrd@z Thu Jan 1 00:00:00 1970 From: Caitlin Bestler Subject: Re: strong ordering for data registered memory Date: Thu, 12 Nov 2009 13:51:40 PST Message-ID: <47893.1258062700@asomi.com> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 8BIT Return-path: Content-Disposition: inline Sender: linux-rdma-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: David Brean , Jason Gunthorpe Cc: Richard Frank , Roland Dreier , linux-rdma List-Id: linux-rdma@vger.kernel.org >On Thu Nov 12 12:43 , David Brean wrote:See section 4 in the paper called "High Performance RDMA Based MPI Implementation over InfiniBand" on the MVAPICH web page for description of one implementation that polls on data buffers. Specifically, look at text around the statement "Although the approach uses the in-order implementation of hardware for RDMA write which is not specified in the InfiniBand standard, this feature is very likely to be kept by different hardware designers." Although this paper is describing a PCI-X implementation, the feature is also exists on PCIe. > >It's assumed that the host memory interconnect complies with statements described in the "Update Ordering and Granularity Provided by a Write Transaction" of the PCI spec. This particular application depends on PCI WRITE behavior, not READ. > >Does this help? > A simplified way of looking at this requirement is that the last N bytes of the RDMA Write payload require the same ordering guarantees as a CQE would have had. This is of course ironic since the technique was developed to avoid the overhead of the CQ. -- To unsubscribe from this list: send the line "unsubscribe linux-rdma" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html