linux-kernel - Re: [RFC PATCH] time: Support in tick broadcast framework for archs without an external wakeup source

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Date:	Fri, 13 Dec 2013 10:51:23 +0530
From:	Preeti U Murthy <preeti@...ux.vnet.ibm.com>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
CC:	peterz@...radead.org, fweisbec@...il.com,
	paul.gortmaker@...driver.com, paulus@...ba.org, mingo@...nel.org,
	shangw@...ux.vnet.ibm.com, rafael.j.wysocki@...el.com,
	paulmck@...ux.vnet.ibm.com, arnd@...db.de,
	linux-pm@...r.kernel.org, rostedt@...dmis.org,
	michael@...erman.id.au, john.stultz@...aro.org, tglx@...utronix.de,
	chenhui.zhao@...escale.com, deepthi@...ux.vnet.ibm.com,
	r58472@...escale.com, geoff@...radead.org,
	linux-kernel@...r.kernel.org, srivatsa.bhat@...ux.vnet.ibm.com,
	schwidefsky@...ibm.com, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [RFC PATCH] time: Support in tick broadcast framework for archs
 without an external wakeup source

Hi Ben,

On 12/13/2013 10:47 AM, Benjamin Herrenschmidt wrote:
> On Fri, 2013-12-13 at 09:49 +0530, Preeti U Murthy wrote:
>> On some architectures, in certain CPU deep idle states the local timers stop.
>> An external clock device is used to wakeup these CPUs. The kernel support for the
>> wakeup of these CPUs is provided by the tick broadcast framework by using the
>> external clock device as the wakeup source.
> 
>> However on architectures like PowerPC there is no external clock device. 
> 
> Minor nit ...
> 
> I wouldn't make this an architectural statement. Some PowerPC's do have
> external clock devices (for example the old MPIC interrupt controller
> had timers). In fact, if we really need it, I'm sure we *could* find
> something somewhere in P8 that could act as a timer, probably hijacking
> a bit of the OCC or similar but at this stage, that's not on the radar.
> 
> So make it an implementation statement. "However, not all
> implementations, such as some PowerPC ones, provide such an external
> timer ...".

Thanks for this information. I will update this going ahead.

Regards
Preeti U Murthy

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