Messages in this thread | | | Date | Thu, 11 Oct 2007 17:05:40 +0530 | Subject | Re: gigabit ethernet power consumption | From | "K.Prasad" <> |
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On Wed, 10 Oct 2007 00:11:17 +0530, Kok, Auke <auke-jan.h.kok@intel.com> wrote:
> Lennart Sorensen wrote: >> On Mon, Oct 08, 2007 at 03:31:51PM -0700, Kok, Auke wrote: >>> you most certainly want to do this in userspace I think. >>> >>> One of the biggest problems is that link negotiation can take a >>> significant amount >>> of time, well over several seconds (1 to 3 seconds typical) with >>> gigabit, and >>> having your ethernet connection go offline for 3 seconds may not be >>> the desired >>> effect for when you want to get more bandwidth in the first place. >>> >>> However, when a laptop is in battery mode, switching down from gigabit >>> to 100mbit >>> makes a lot more sense, so this is something I would recommend. This >>> can be as >>> easy as changing the advertisement mask of the interface and >>> renegotiating the >>> link. Userspace could handle that very easily. >> >> Now if you were trying to transfer a lot of data to the laptop, would it >> be more power efficient to do it at gigabit speeds so you can finish >> sooner and shut down the machine entirely, or to slow to 100mbit and >> take longer to do it, and hence spend more time powering the cpu and >> ram? > > my suspicion is that the cost of switching is much higher than what you > would > consume running at 100mbit, even if the amount of data is quite large. > going > offline to renegotiate the link would already cost you 3W typically. > > I definately think that userspace is the right field to solve this > problem: let > the users decide how to use the available power on their sytems through > a decent > power profile tool (perhaps gnome-power-manager or something like that). > This way > the user can choose. > > Auke > -
Perhaps interrupt moderation could be of help here (say - switch to lesser interrupts per unit of time when running on battery), which I find that the e1000 driver doesn't employ in the kernel presently. (For interrupt moderation, refer: http://download.intel.com/design/network/applnots/ap450.pdf.)
Without the side-effect of experiencing a link-flap when switching to a lower-speed (with its toll in terms of down-time for auto-negotiation, STP, etc), the Interrupt Moderation Algorithm dynamically adjusts the number of interrupts based on traffic - and presumably consume less power. For an "Optimise for Power" kind of profile - the driver can be loaded with a higher throttle rate during boot-time.
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