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Re: Request for feedback and/or participation on https://fedoraproject.org/wiki/Features/PowerManagement



On Wed, Feb 04, 2009 at 05:04:56PM +0100, Phil Knirsch wrote:

> Network card speeds and harddisk spindowns is a bit tricker imo, though 
> we probably could enable a higher powersave mode for harddisk by default 
> at least in case a user wants to save power. Some of this is/will be 
> addressed by the tuned i'm working on which monitors the usage of 
> network and harddisk devices and dynamically adapts the settings to the 
> current use.

The problem with network card retraining is that you lose link for a 
significant period of time, which is a pain (especially if you want to 
retrain upwards because you're trying to send a pile of data...). Hard 
drive APM has some irritating behavioural aspects - a lot of drives will 
unload the heads very aggressively, which can cause you to hit SMART 
thresholds in 6 months or so of normal use. We probably want to talk to 
vendors about that.

Hard drive spindown is an interesting problem that I've been looking 
into. There's a lot of published work on adaptive algorithms for this, 
but the most interesting is the Helmbold one. Unfortunately, it doesn't 
actually seem to work - the behaviour is dependent on the number of 
experts in the system, when really it should be invarient of that.

> Laptop mode and a higher value for dirty_writeback_centisecs, there i'm 
> personally torn a bit myself. I personally do use it on all my machines 
> (laptop and desktop), but i can understand people who are a bit paranoid 
> about their data integrity not wanting to have that by default. But i'd 
> personally be all for going that way.

Anyone interested in data integrity should be calling fsync() at 
appropriate times. I'd be entirely in favour of bumping that up to 5 
minutes or so.

> In regard to relatime from what i've found so far we seem to be doing 
> that already by default it seems, though i'd like to have that verified.

We're not right now. The in-kernel relatime code results in everything 
in /tmp getting deleted by tmpreaper because it has no idea that files 
are being read. Ingo wrote a patch to work around this - I've been 
trying to push that upstream, but it got about as bikeshedded as the 
cursor thing. I'll give that another go this cycle. We should probably 
merge it for F11 anyway since the code is trivial.

> Then disabling CD-ROM polling is definitely something for the ServerSIG, 
> but on a default Desktop i think the user experience would suffer if we 
> would do that by default.

Yeah. Best not to.

> Enabling USB autosuspend looks like a good candidate for being a default 
> though. I've used it on quite a few Fedora 10 machines around here and 
> haven't experienced any problems so far, so it seems to have matured 
> enough by now from what i can see.

Scanners and printers are the worst case for this. I think we really 
need to implement some kind of decent testing framework and build some 
whitelists.

> Last but not least the dpms off, i think that should definitely be part 
> of the Desktop screensaver defaults, especially if you look at how much 
> power a modern LCD display eats when it's only dimmed down to black.

Absolutely. If the default screensaver is "blank" then we should be 
entering DPMS very aggressively. I don't see any need for this to be 
configurable. I'm working on adaptive screensaver behaviour that should 
prevent this being something that has a noticable impact on the user.

-- 
Matthew Garrett | mjg59 srcf ucam org


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