linux-kernel - Re: [PATCH v2] ring-buffer: Replace this_cpu_*() with __this_cpu

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Message-ID: <20150317144701.GJ10068@pengutronix.de>
Date:	Tue, 17 Mar 2015 15:47:01 +0100
From:	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Christoph Lameter <cl@...ux.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	linux-arm-kernel@...ts.infradead.org,
	Russell King <linux@....linux.org.uk>
Subject: Re: [PATCH v2] ring-buffer: Replace this_cpu_*() with __this_cpu_*()

Guten Morgen Steven,

On Tue, Mar 17, 2015 at 10:40:38AM -0400, Steven Rostedt wrote:
>  static __always_inline void trace_recursive_unlock(void)
>  {
> -	unsigned int val = this_cpu_read(current_context);
> +	unsigned int val = __this_cpu_read(current_context);
> +	unsigned int val2;
>  
> -	val--;
> -	val &= this_cpu_read(current_context);
> -	this_cpu_write(current_context, val);
> +	val2 = val - 1;
> +	val &= val2;
> +	__this_cpu_write(current_context, val);
You could use:

	unsigned int val = __this_cpu_read(current_context);

	val = val & (val - 1);

	__this_cpu_write(current_context, val);

and save a few lines and still make it more readable (IMHO).

BTW, this patch makes the additional lines in the trace disappear, so if
you think that makes a Tested-by applicable, feel free to add it.

Best regards
Uwe
-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |
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