From mboxrd@z Thu Jan 1 00:00:00 1970 From: Haggai Eran Subject: Re: [PATCH RFC 1/1] Add support for ZONE_DEVICE IO memory with struct pages. Date: Thu, 17 Mar 2016 17:18:11 +0200 Message-ID: <56EACAB3.5070301@mellanox.com> References: <1457979277-26791-1-git-send-email-stephen.bates@pmcs.com> <20160314212344.GC23727@linux.intel.com> <20160314215708.GA7282@obsidianresearch.com> Mime-Version: 1.0 Content-Type: text/plain; charset="windows-1252" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20160314215708.GA7282-ePGOBjL8dl3ta4EC/59zMFaTQe2KTcn/@public.gmane.org> Sender: linux-rdma-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Jason Gunthorpe , Matthew Wilcox Cc: Stephen Bates , linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org, linux-rdma-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-nvdimm-y27Ovi1pjclAfugRpC6u6w@public.gmane.org, javier-rmLALz0KWFtWk0Htik3J/w@public.gmane.org, sagig-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org, leonro-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org, artemyko-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org, hch-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org List-Id: linux-rdma@vger.kernel.org On 3/14/2016 11:57 PM, Jason Gunthorpe wrote: > The other issue is that the fencing mechanism RDMA uses to create > ordering with system memory is not good enough to fence peer-peer > transactions in the general case. It is only possibly good enough if > all the transactions run through the root complex. Are you sure this is a problem? I'm not sure it is clear in the PCIe specs, but I thought that for transactions that are not relaxed-ordered and don't use ID-based ordering, a PCIe switch must prevent reads and writes from passing writes. I assume this is true even when the requestor ID is different because IDO relaxes these constraints specifically for transactions coming from different requestor IDs. Regards, Haggai -- 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