linux-kernel - Re: [OLPC-devel] Re: [RFC][PATCH 1/2] ACPI: Idle Processor PM Improvements

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Date:	Mon, 4 Sep 2006 13:09:33 +0000
From:	Pavel Machek <pavel@....cz>
To:	Jim Gettys <jg@...top.org>
Cc:	Bjorn Helgaas <bjorn.helgaas@...com>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	"Brown, Len" <len.brown@...el.com>,
	Linux Kernel ML <linux-kernel@...r.kernel.org>,
	Dominik Brodowski <linux@...inikbrodowski.net>,
	ACPI ML <linux-acpi@...r.kernel.org>,
	Adam Belay <abelay@...ell.com>,
	"Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>,
	Arjan van de Ven <arjan@...ux.intel.com>, devel@...top.org
Subject: Re: [OLPC-devel] Re: [RFC][PATCH 1/2] ACPI: Idle Processor PM Improvements

Hi!

> In short, we have novel hardware: we can have our screen on, and suspend
> the processor to RAM, and use a half a watt.  We can have our wireless
> forwarding packets in our mesh networks, with the processor suspended,
> consuming under 400mw (we hope 300mw by the time we ship).  Both on, and
> we're still under one watt.
> 
> For keyboard activity, human perception is in the 100-200 millisecond
> range; for some other stuff, it is even less much than that.  So that's
> the necessity; now the invention.
> 
> I've done a straw pole among kernel gurus at OLS and elsewhere on how
> fast Linux might be able to resume. I've gotten answers of typically
> "one second".
> 
> But, on other platforms (see attached), I have data I've measured myself
> showing Linux going from resume from RAM to *scheduling user level
> processes* 100 times faster than that, on a wimpy 200mhz ARM processor.
> Yes, Matilda, Linux can, on non-braindead hardware, resume all the way
> to scheduling user processes in 10 milliseconds on a 200mhz processor.

2.4 and 2.6 are *very* different here. You'll probably need to optimize freezer
in 2.6 a bit...
							Pavel
-- 
Thanks for all the (sleeping) penguins.
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