The PowerClamp driver

Posted Dec 6, 2012 13:56 UTC (Thu) by Jonno (subscriber, #49613)
In reply to: The PowerClamp driver by ras
Parent article: The PowerClamp driver

> Can someone with a clue tell me what is really going on?
Linux kernel CPU power management currently beats all other, but the CPU isn't the only thing drawing power. GPU, PCIe, and HDD power management are all areas where Linux could do significantly better. And Linux userspace is typically less power management aware than that of MacOS X, resulting in the Mac simply doing less work while on battery...

The PowerClamp driver

Posted Dec 7, 2012 1:59 UTC (Fri) by idupree (guest, #71169) [Link] (1 responses)

Yeah, alas. I'd hoped it was a "[mechanism] to put an overall limit on the amount of power consumed" but it isn't. I was looking at certain external batteries[*] for travel which have a maximum output rating of 4.2A. My laptop (at 19V DC input) is capable of using more than 4.2A (80 W). The power brick it came with has max 6.32A; from my measurements with some of CPU/GPU/screen at full force, this higher capacity is sometimes necessary. If my system tried to draw more power at any moment, bad things might happen (I'm not sure how bad. Battery damage? Laptop shutdown?). I wouldn't buy that battery without a way to ensure the laptop's total power usage was below the limit -- which is a hard problem which this article does not appear to go anywhere near solving.

[*] http://zikko-store.com/product_view.php?id=7

The PowerClamp driver

Posted Dec 12, 2012 16:40 UTC (Wed) by arjan (subscriber, #36785) [Link]

powerclamp is a building block towards a solution that you describe.
Note that if you need a "near instant" limit, a kernel level solution isn't going to work, you need something much much faster responding.
But if you can deal with "we need over <some hundreds of milliseconds> the average to be below X", and you can measure X.. this driver is what a small (userspace) control agent can use to actually impact the current consumption