Re: [PATCH 11/23] clocksource: atomic signals

[Ingo Molnar <mingo@elte.hu>]

* Daniel Walker <dwalker@mvista.com> wrote:

> Modifies the way clocks are switched to in the timekeeping code. The 
> original code would constantly monitor the clocksource list checking 
> for newly added clocksources. I modified this by using atomic types to 
> signal when a new clock is added. This allows the operation to be used 
> only when it's needed.

I see little difference between your and John's code: both poll 
something - you poll an atomic "did a new clocksource arrive" flag in 
the timer interrupt, John takes the clocksource_lock spinlock and checks 
a "did a new clocksource arrive" variable. Both are global atomic 
variables in essence.

what i'd see as a real cleanup here would be to get away from this 'poll 
whether there's any clocksource update' model, and to just ensure that a 
running timer irq will always see the latest clocksource. I.e. to run 
the change_clocksource() logic (and the following updates) when a new 
clock source is selected - not when the next timer interrupt runs. That 
would propagate all effects of a new clock source immediately.

	Ingo