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

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Message-ID: <20100210021303.GA5079@linux.vnet.ibm.com>
Date:	Wed, 10 Feb 2010 07:43:03 +0530
From:	Arun R Bharadwaj <arun@...ux.vnet.ibm.com>
To:	Randy Dunlap <rdunlap@...otime.net>
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,
	Arun Bharadwaj <arun@...ux.vnet.ibm.com>
Subject: Re: [v11 PATCH 1/9]: cpuidle: Design documentation patch

* Randy Dunlap <rdunlap@...otime.net> [2010-02-09 09:00:54]:

> 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.
> 

Here, it means between. Will remove the abbreviation since it might be
confusing.

> 
> > +
> > +
> > +-----------------					-----------------
> > +|		|					|  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/
>

noted.

thanks
arun

> > +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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