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

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Date:	Wed, 31 Jan 2007 11:17:10 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Daniel Walker <dwalker@...sta.com>
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


* 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).

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.

thirdly, CLOCKSOURCE_NOTIFY_FREQ is totally unused as well.

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

	Ingo
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