From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jason Gunthorpe Subject: TCP CUBIC and IPoIB Date: Mon, 8 Nov 2010 17:58:13 -0700 Message-ID: <20101109005813.GD909@obsidianresearch.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline Sender: linux-rdma-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: "linux-rdma-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" List-Id: linux-rdma@vger.kernel.org I wonder if anyone has ever looked at this? It looks like there is something wrong here. I was just looking at some results from a stock 2.6.35 kernel doing TCP over IPoIB (2k MTU) and CUBIC looks like it is going nutz, you can see in a bandwidth plot a fairly characteristic saw tooth pattern, and diminished bandwidth. The effect compounds rather dramatically as the RTT goes up. This isn't really my area of expertise, so I wonder if someone else has looked into this? Errant congestion events will sap bandwidth even on low latency links.. Cheers, Jason -- 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