From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ben Hutchings Subject: Re: Default offload settings in Ethernet drivers Date: Thu, 11 Dec 2008 19:29:28 +0000 Message-ID: <1229023768.3006.37.camel@achroite> References: <49415EDB.3030006@computer.org> <20081211105459.3e615be8@s6510> Mime-Version: 1.0 Content-Type: text/plain Content-Transfer-Encoding: 7bit Cc: Stephen Hemminger , netdev@vger.kernel.org To: Jan Ceuleers Return-path: Received: from smarthost03.mail.zen.net.uk ([212.23.3.142]:48704 "EHLO smarthost03.mail.zen.net.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759988AbYLKT3h (ORCPT ); Thu, 11 Dec 2008 14:29:37 -0500 In-Reply-To: <20081211105459.3e615be8@s6510> Sender: netdev-owner@vger.kernel.org List-ID: On Thu, 2008-12-11 at 10:54 -0800, Stephen Hemminger wrote: > On Thu, 11 Dec 2008 19:41:31 +0100 > Jan Ceuleers wrote: > > > Hi! > > > > A discussion recently took place on the power mailing list on the > > subject of the impact of (hardware-assisted) offload functions on the > > power efficiency of the overall system. > > > > The discussion was brought on by me noticing that not all drivers enable > > all of their offload features by default (case in point: r8169). > > > > Although the discussion may not be complete, early indications are that: > > > > 1. Hardware-assisted offloads improve power efficiency unless > > implemented in a separate CPU (TOE / Total Offloading); > > > > 2. It would probably be a good idea to enable hardware-assisted offloads > > other than TOE by default given the above. > > > > I would therefore like to sollicit views here: > > > > 1. Would changing default offload settings in Ethernet drivers help to > > save the planet? > > > > 2. Which offload settings does it make sense to enable by default? > > Go get a kill-a-watt meter and real hardware and measure. [...] Even then, the results will be highly dependent on the CPU's power- saving capabilities and on settings that affect the pattern of IRQs like interrupt moderation and number of queues used by multiqueue-capable drivers, not just on the offload settings. I would expect checksum generation/validation and segmentation in an ASIC to take less power than in a CPU, but on an already-busy CPU this might not be the case. Power usage also depends on throughput, of course. If the test involves pushing data as fast as possible rather than simulating a specific workload then offload features may well probably increase throughput without reducing power consumption. So maybe the metric should be power/throughput... but there is unlikely to be a linear relationship between the two, so a single figure for this may be misleading. Ben. -- Ben Hutchings, Senior Software Engineer, Solarflare Communications Not speaking for my employer; that's the marketing department's job. They asked us to note that Solarflare product names are trademarked.