linux-kernel - Re: [RFC][PATCH 0/3] A Dynticks Aware Processor Idle PM Governor

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Date:	Thu, 31 May 2007 21:17:48 -0400
From:	Len Brown <lenb@...nel.org>
To:	Adam Belay <abelay@...ell.com>
Cc:	Len Brown <len.brown@...el.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...l.org>,
	Shaohua Li <shaohua.li@...el.com>, Pallipadi@...r.kernel.org,
	Venkatesh <venkatesh.pallipadi@...el.com>,
	linux-acpi@...r.kernel.org
Subject: Re: [RFC][PATCH 0/3] A Dynticks Aware Processor Idle PM Governor

Applied this series to acpi-test
in anticipation that Venki is about to send some incremental
patches to address the feedback on it.

thanks,
-Len

On Saturday 24 March 2007 03:46, Adam Belay wrote:
> Hi All,
> 
> Here is my first take at implementing an idle PM governor that takes
> full advantage of NO_HZ.  I call it the 'menu' governor because it
> considers the full list of idle states before each entry.
> 
> I've kept the implementation fairly simple.  It attempts to guess the
> next residency time and then chooses a state that would meet at least
> the break-even point between power savings and entry cost.  To this end,
> it selects the deepest idle state that satisfies the following
> constraints:
>      1. If the idle time elapsed since bus master activity was detected
>         is below a threshold (currently 20 ms), then limit the selection
>         to C2-type or above.
>      2. Do not choose a state with a break-even residency that exceeds
>         the expected time remaining until the next timer interrupt.
>      3. Do not choose a state with a break-even residency that exceeds
>         the elapsed time between the last pair of break events,
>         excluding timer interrupts.
> 
> This governor has an advantage over "ladder" governor because it
> proactively checks how much time remains until the next timer interrupt
> using the tick infrastructure.  Also, it handles device interrupt
> activity more intelligently by not including timer interrupts in break
> event calculations.  Finally, it doesn't make policy decisions using the
> number of state entries, which can have variable residency times (NO_HZ
> makes these potentially very large), and instead only considers sleep
> time deltas.
> 
> The menu governor can be selected during runtime using the cpuidle sysfs
> interface like so:
> "echo "menu" > /sys/devices/system/cpu/cpuidle/current_governor"
> 
> This patchset applies against 2.6.21-rc4 plus the latest from the acpi
> testing tree, which is available here:
> ftp://ftp.kernel.org/pub/linux/kernel/people/lenb/acpi/patches/test/2.6.21/acpi-test-20070126-2.6.21-rc4.diff.bz2
> 
> I'd really appreciate any comments, benchmarks, or suggestions.
> 
> Cheers,
> Adam
> 
> 
> -
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