linux-kernel - Re: [PATCH 5/7] time: Shadow cycle

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Message-ID: <20120228081659.GF21106@elte.hu>
Date:	Tue, 28 Feb 2012 09:16:59 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	John Stultz <john.stultz@...aro.org>
Cc:	lkml <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Richard Cochran <richardcochran@...il.com>
Subject: Re: [PATCH 5/7] time: Shadow cycle_last in timekeeper structure

* John Stultz <john.stultz@...aro.org> wrote:

> @@ -184,7 +186,7 @@ static inline s64 timekeeping_get_ns(void)
>  	cycle_now = clock->read(clock);
>  
>  	/* calculate the delta since the last update_wall_time: */
> -	cycle_delta = (cycle_now - clock->cycle_last) & clock->mask;
> +	cycle_delta = (cycle_now - timekeeper.cycle_last) & clock->mask;

Just a general code design observation: the way how the global 
'timekeeper' structure is accessed is rather ugly.

The standard method is to pass it in to timekeeping_get_ns() 
(and other methods) as a parameter, with the highest level 
taking the address via &timekeeping.

That will also make the code shorter and more obvious: the 
familar tk->cycle_last pattern instead of the current mixed uses 
of timekeeping.cycle_last and tk->cycle_last.

There's many similar patterns throughout this code, they need to 
be fixed as well.

Thanks,

	Ingo
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