Rethinking power-aware scheduling
Posted Jan 13, 2012 23:23 UTC (Fri) by dlang (subscriber, #313)
on their laptops, when they unplug the screen dims slightly and the systems switch to a more aggressive power saving mode.
your customers are not asking for it explicitly because they are used to getting it by default.
most of them won't realise what the problem is if they don't get it, they will just consider their device sluggish (or at least not as fast as the competition) if they don't get peak performance when plugged in, and they will consider the device/OS to be a power hog if it doesn't last as long when on battery power.
Posted Jan 13, 2012 23:28 UTC (Fri) by mjg59 (subscriber, #23239)
Posted Jan 13, 2012 23:39 UTC (Fri) by dlang (subscriber, #313)
Posted Jan 13, 2012 23:44 UTC (Fri) by mjg59 (subscriber, #23239)
Posted Jan 14, 2012 0:02 UTC (Sat) by dlang (subscriber, #313)
But setting aggressive power management for all cases as the default for everyone is wrong.
Posted Jan 14, 2012 22:43 UTC (Sat) by raven667 (subscriber, #5198)
Posted Jan 14, 2012 22:48 UTC (Sat) by dlang (subscriber, #313)
it takes time to bring CPUs out of sleep states, and during that time the work that is waiting for them may not be able to get done.
it is not always less power to run at full speed and then sleep, that is frequently the case, but it depends on the ability to move in and out of sleep, along with the amount of power saved.
In this case, we are talking about the options when you have multiple cores, some sharing components, and have less work than it takes to max out all the cores.
putting all the work on one core and powering off the other cores may save power, but it could make the work take longer (but not enough longer to use more power than the other cores would consume if they were not powered down). for some people having the work take slightly longer won't matter, for others it will.
Posted Jan 15, 2012 3:53 UTC (Sun) by raven667 (subscriber, #5198)
Posted Jan 15, 2012 13:48 UTC (Sun) by mjg59 (subscriber, #23239)
Posted Jan 15, 2012 11:09 UTC (Sun) by liljencrantz (guest, #28458)
My somewhat limited personal experience is that most data centers I've worked with have a total power limit per rack that is painfully low, and that reducing power usage by a few watts per system would allow us to stuff in one more server per rack, leading to a significant amount of savings. This resonates well with what Garret is saying.
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