Date: Wed, 31 Jan 2007 12:07:23 +0100
From: Ingo Molnar <mingo@elte.hu>
To: Daniel Walker <dwalker@mvista.com>
Cc: akpm@osdl.org, linux-kernel@vger.kernel.org, johnstul@us.ibm.com
Subject: Re: [PATCH 11/23] clocksource: atomic signals
Message-ID: <20070131110722.GA1847@elte.hu>
References: <20070131033710.420168478@mvista.com> <20070131033806.468210824@mvista.com>
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* 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
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