* Re: [linux-pm] power draw depending on PHY speed
2009-08-28 19:03 ` [linux-pm] power draw depending on PHY speed Rafael J. Wysocki
@ 2009-08-28 19:29 ` Ben Hutchings
0 siblings, 0 replies; 2+ messages in thread
From: Ben Hutchings @ 2009-08-28 19:29 UTC (permalink / raw)
To: Rafael J. Wysocki; +Cc: Leisner, Martin, linux-pm, martyleisner, NetDEV list
On Fri, 2009-08-28 at 21:03 +0200, Rafael J. Wysocki wrote:
> On Friday 28 August 2009, Leisner, Martin wrote:
> > While doing some current probe measurements (i.e. to measure the effects
> > of NAP and frequency scaling with a freescale processor) I noticed some
> > very
> > significant differents if we ran on 100Mbit of 1000Mbit ethernet.
> >
> > The hardware guys like at their data sheets and agreed.
> >
> > Does anyone "drop ethernet speed" to save power?
> > (when a system is idle, is isn't necessary to run 1G ethernet).
>
> I don't know, really. This is a netdev question IMO (CC added).
Doing this through the existing autonegotiation mechanism is a bad idea,
because it requires bringing the link down, possibly for a few seconds.
There is a standard on the way (802.3az, aka Energy-Efficient Ethernet
or EEE) which will allow for speed renegotiation without dropping the
link.
> > When a system has WOL capability, what speed does it run at when the
> > system is sleeping?
>
> That's a very good question. I bet that depends on the NIC in question, at
> least I'm not sure if any spec regulates it.
I'm not aware of a spec, but generally a 1G or 10G multi-speed PHY will
not advertise speeds higher than 100 Mbit/s when sleeping.
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.
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