From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jason Gunthorpe Subject: Re: Size of Infiniband packets Date: Thu, 5 Dec 2013 16:53:34 -0700 Message-ID: <20131205235334.GC20137@obsidianresearch.com> References: Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-rdma-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Anuj Kalia Cc: "linux-rdma-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" List-Id: linux-rdma@vger.kernel.org On Thu, Dec 05, 2013 at 06:22:57PM -0500, Anuj Kalia wrote: > I'm trying to do a back-of-the-hand calculation of the number of > packets per second that can be transmitted over 40Gbps Infiniband. I > need some information about the packet size to do this calculation. > > Suppose I do an 8 byte RDMA write over RC transport. What is the > packet size that is transmitted on the wire? This should include > Infiniband headers and the work request. See page 257 (Figure 76) of IB Spec volume 1. A RDMA write will contain: LRH 8 BTH 12 RETH 16 data 8 ICRC 4 VCRC 2 Plus 2 bytes of framing is 52 bytes. IB is defined to sustain continuous back-to-back packets, so 3200MB/sec / 52 bytes/packet = 615 million pkts/sec -- Jason Gunthorpe (780)4406067x832 Chief Technology Officer, Obsidian Research Corp Edmonton, Canada -- 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