linux-kernel - Re: gigabit ethernet power consumption

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Date:	Fri, 12 Oct 2007 09:35:15 -0700
From:	"Kok, Auke" <auke-jan.h.kok@...el.com>
To:	7eggert@....de
CC:	Kok@...p.glb.intel.com, prasad@...ux.vnet.ibm.com,
	Lennart Sorensen <lsorense@...lub.uwaterloo.ca>,
	Pavel Machek <pavel@....cz>,
	Arjan van de Ven <arjan@...radead.org>,
	kernel list <linux-kernel@...r.kernel.org>
Subject: Re: gigabit ethernet power consumption

Bodo Eggert wrote:
> Kok, Auke <auke-jan.h.kok@...el.com> wrote:
>> K.Prasad wrote:
> 
>>> 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.
>> We're changing this to be run-time adjustable in newer drivers.
>>
>> However, the power consumed by your nic staying in gigabit mode is much
>> greater in the long run then what you can save by trying to scrounge for
>> milliwatts reducing interrupts generated by the nic. By default it already
>> moderates them somewhat. Practically this feature is really not useful for
>> powersaving, it just won't add up to actual benefits in a real life situtation
>> I think.
> 
> Just a thought:
> How much power does a non-connected NIC consume, and can you save power
> by forcing 10 MBit until a link is detected (doubling negotiation time)?

no, the PHY consumes a minimal amount of energy when not connected, regardless of
whether it is advertising 10, 100 or 1000mbit.

Cheers,

Auke
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