[PATCH v2 00/15] Make SMP timers standalone

[Marc Zyngier]

On 04/01/12 21:47, Russell King - ARM Linux wrote:
> On Wed, Jan 04, 2012 at 05:39:16PM +0000, Marc Zyngier wrote:
>> On 22/12/11 19:32, Russell King - ARM Linux wrote:
>>> You're also aware I assume that local timers are different from the global
>>> timer itself, and require to have additional callbacks for broadcasting
>>> the global timer tick?
>>
>> I was under the impression that we either have the global timer together
>> with broadcasting or the local timers. Completely removing the broadcast
>> callback doesn't seem to generate any ill effect as long as the local
>> timers are used instead of the global timer (which of course requires
>> broadcast in the SMP configuration).
> 
> I believe even if you have local timers, there are situations where the
> these will be disabled and the kernel will switch to broadcasting from a
> global timer tick.  I think such a scenario would be like that encountered
> with OMAP, where suspending a CPU stops its TWD - meaning that the TWD
> can't be used to wake the CPU from one of the deeper idle states.

Yes, being able to wake up is definitely a good reason to keep a global
timer around, not to mention other artifacts (TWD calibration being one,
though on its way out thanks to LinusW patch series).

	M.
-- 
Jazz is not dead. It just smells funny...