linux-kernel - Re: [PATCH 09/23] clocksource: add block notifier

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Date:	Wed, 31 Jan 2007 07:25:52 -0800
From:	Daniel Walker <dwalker@...sta.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	akpm@...l.org, linux-kernel@...r.kernel.org, johnstul@...ibm.com,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 09/23] clocksource: add block notifier

On Wed, 2007-01-31 at 11:17 +0100, Ingo Molnar wrote:
> * Daniel Walker <dwalker@...sta.com> wrote:
> 
> > Adds a call back interface for register/rating change events. This is 
> > also used later in this series to signal other interesting events.
> 
> This patch adds:
> 
> > +#define CLOCKSOURCE_NOTIFY_REGISTER	1
> > +#define CLOCKSOURCE_NOTIFY_RATING	2
> > +#define CLOCKSOURCE_NOTIFY_FREQ		4
> 
> and a later patch adds:
> 
> > +#define CLOCKSOURCE_NOTIFY_UNSTABLE	8
> 
> while i tentatively agree with the introduction of clocksource driver 
> notifications in general (given any actual real users of that 
> infrastructure), i can see three problems with your notifier changes:
> 
> firstly, with the full changes applied, CLOCKSOURCE_NOTIFY_RATING is 
> totally unused (and not even driven by the core clocksource code).

True, ratings are constant so the notification never happens (and never
needs to)

> secondly, CLOCKSOURCE_NOTIFY_REGISTER is only used by the core 
> clocksource code and no register-notifier interface is exposed: this 
> makes the whole thing an expensive NOP.

I don't know what you mean when you say "no register-notifier interface
is exposed" .. The timekeeping code doesn't use this notification , but
it really should. It's not that big of an issue since we don't have many
clocks in modules.. 

> thirdly, CLOCKSOURCE_NOTIFY_FREQ is totally unused as well.

Indeed . Consider it dropped.

> (there are tons of examples in the kernel of how to do driver 
> notification APIs properly.)

Are you referring to the comments above , or something else your seeing
in the code?

Daniel

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