linux-kernel - Re: [cpuops inc_return V1 8/9] random: Use this_cpu_inc

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Date:	Mon, 06 Dec 2010 12:11:42 -0600
From:	Matt Mackall <mpm@...enic.com>
To:	Christoph Lameter <cl@...ux.com>
Cc:	Tejun Heo <tj@...nel.org>, akpm@...ux-foundation.org,
	Richard Kennedy <richard@....demon.co.uk>,
	Pekka Enberg <penberg@...helsinki.fi>,
	linux-kernel@...r.kernel.org,
	Eric Dumazet <eric.dumazet@...il.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Subject: Re: [cpuops inc_return V1 8/9] random: Use this_cpu_inc_return

On Mon, 2010-12-06 at 11:40 -0600, Christoph Lameter wrote:
> plain text document attachment (cpuops_inc_return_random)
> __this_cpu_inc can create a single instruction to do the same as
> __get_cpu_var()++.

> -	    (__get_cpu_var(trickle_count)++ & 0xfff))
> +	    ((__this_cpu_inc_return(trickle_count) - 1) & 0xfff))

I see you've added a "- 1" to mimic the post-increment ++ semantic.

The goal of this code to add only 1 sample in every 4096, but we don't
really care which, so this semantic isn't actually important here.

-- 
Mathematics is the supreme nostalgia of our time.


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