linux-kernel - Re: [v11 PATCH 1/9]: cpuidle: Design documentation patch

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Date:	Tue, 09 Feb 2010 09:00:54 -0800
From:	Randy Dunlap <rdunlap@...otime.net>
To:	arun@...ux.vnet.ibm.com
CC:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Ingo Molnar <mingo@...e.hu>,
	Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>,
	Dipankar Sarma <dipankar@...ibm.com>,
	Balbir Singh <balbir@...ibm.com>,
	Venkatesh Pallipadi <venkatesh.pallipadi@...el.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [v11 PATCH 1/9]: cpuidle: Design documentation patch

On 02/09/10 00:29, Arun R Bharadwaj wrote:
> * Arun R Bharadwaj <arun@...ux.vnet.ibm.com> [2010-02-09 13:58:16]:
> 
> This patch adds a little information about the redesigned cpuidle
> infrastructure in Documentation/cpuidle/core.txt
> 
> Signed-off-by: Arun R Bharadwaj <arun@...ux.vnet.ibm.com>
> ---
>  Documentation/cpuidle/core.txt |   35 +++++++++++++++++++++++++++++++++++
>  1 file changed, 35 insertions(+)
> 
> Index: linux.trees.git/Documentation/cpuidle/core.txt
> ===================================================================
> --- linux.trees.git.orig/Documentation/cpuidle/core.txt
> +++ linux.trees.git/Documentation/cpuidle/core.txt
> @@ -21,3 +21,38 @@ which can be used to switch governors at
>  is meant for developer testing only. In normal usage, kernel picks the
>  best governor based on governor ratings.
>  SEE ALSO: sysfs.txt in this directory.
> +
> +Design:
> +
> +Cpuidle allows for registration of multiple sets of idle routines.
> +The latest registered set is used by cpuidle governors as the current
> +active set to choose the right idle state. This set is managed as a
> +list and each time the newly registered set is added to the head of the
> +list and made the current active set.
> +
> +An example of how this would work on x86 is shown below.
> +
+-----------------					-----------------
+|		|					|		|
+| choose b/w	|	mwait is chosen			|    mwait	|
+| mwait, poll,	|-------------------------------------> |(current active|
+| default, c1e	|	register to cpuidle		|    set)	|
+|		|	with mwait as the idle routine	|		|
+-----------------					-----------------

What is "b/w" above?  "between"?  I've see "btw" used a few times as an
abbreviation for between, but I don't recall ever seeing b/w.
OTOH, I have seen b/w used for bandwidth.


> +
> +
> +-----------------					-----------------
> +|		|					|  c1, c2, c3	|
> +|     ACPI	|	register to cpuidle		|   (current)	|
> +|   discovery	|-------------------------------------> |---------------|
> +|		|	with c1, c2, c3			|     mwait	|
> +|		|	as set of idle routines		|		|
> +-----------------					-----------------
> +
> +With this mechanism, a module can register and unregister its set of
> +idle routines at run time in a clean manner.
> +
> +The main idle routine called inside cpu_idle() of every arch is defined in
> +driver/cpuidle/cpuidle.c which would in turn call the idle routine selected

   drivers/

> +by the governor. If the CONFIG_CPU_IDLE is disabled, the arch needs to
> +provide an alternate definition for cpuidle_idle_call().


-- 
~Randy
--
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