linux-kernel - Re: [RFC PATCH 5/6] implement per-cpu&per-domain state machine call

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Date:	Tue, 06 Mar 2012 11:58:18 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Lai Jiangshan <laijs@...fujitsu.com>
Cc:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org, mingo@...e.hu, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...ymtl.ca,
	josh@...htriplett.org, niv@...ibm.com, tglx@...utronix.de,
	rostedt@...dmis.org, Valdis.Kletnieks@...edu, dhowells@...hat.com,
	eric.dumazet@...il.com, darren@...art.com, fweisbec@...il.com,
	patches@...aro.org
Subject: Re: [RFC PATCH 5/6] implement per-cpu&per-domain state machine
 call_srcu()

On Tue, 2012-03-06 at 17:57 +0800, Lai Jiangshan wrote:
>  /*
> + * 'return left < right;' but handle the overflow issues.
> + * The same as 'return (long)(right - left) > 0;' but it cares more.

About what? And why? We do the (long)(a - b) thing all over the kernel,
why would you care more?

> + */
> +static inline
> +bool safe_less_than(unsigned long left, unsigned long right, unsigned long max)
> +{
> +       unsigned long a = right - left;
> +       unsigned long b = max - left;
> +
> +       return !!a && (a <= b);
> +} 
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