From mboxrd@z Thu Jan 1 00:00:00 1970 From: "David Laight" Subject: RE: [PATCH] mlx4_en: map entire pages to increase throughput Date: Tue, 17 Jul 2012 13:42:04 +0100 Message-ID: References: <1342458113-10384-1-git-send-email-cascardo@linux.vnet.ibm.com><50044F1D.6000703@hp.com> <20120716.222903.367603216293954363.davem@davemloft.net> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 8BIT Cc: , , , , , , , To: "David Miller" , Return-path: Received: from mx0.aculab.com ([213.249.233.131]:37637 "HELO mx0.aculab.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1753177Ab2GQMms convert rfc822-to-8bit (ORCPT ); Tue, 17 Jul 2012 08:42:48 -0400 Received: from mx0.aculab.com ([127.0.0.1]) by localhost (mx0.aculab.com [127.0.0.1]) (amavisd-new, port 10024) with SMTP id 03633-07 for ; Tue, 17 Jul 2012 13:42:45 +0100 (BST) Content-class: urn:content-classes:message In-Reply-To: <20120716.222903.367603216293954363.davem@davemloft.net> Sender: netdev-owner@vger.kernel.org List-ID: > > That seems rather extraordinarily low - Power7 is supposed to be a > > rather high performance CPU. The last time I noticed O(3Gbit/s) on > > 10G for bulk transfer was before the advent of LRO/GRO - that was in > > the x86 space though. Is mapping really that expensive with Power7? > > Unfortunately, IOMMU mappings are incredibly expensive. I see effects > like this on Sparc too. Would there be any mileage in permanently allocating IOMMU virtual address to the ring entries, then 'just' assigning the correct physical address during rx/tx setup? A long time ago it used to be much faster on sparc systems to receive into a permanently mapped buffer area and then do a maximally aligned copy into the actual rx buffer. David