linux-kernel - Re: [PATCH v4 2/8] init.h: add __read_mostly to early_param_on

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Date:	Thu, 30 Apr 2015 18:00:44 +0200
From:	Borislav Petkov <bp@...e.de>
To:	"Luis R. Rodriguez" <mcgrof@...not-panic.com>
Cc:	mingo@...e.hu, tglx@...utronix.de, hpa@...or.com,
	plagnioj@...osoft.com, tomi.valkeinen@...com,
	daniel.vetter@...el.com, airlied@...ux.ie, dledford@...hat.com,
	awalls@...metrocast.net, syrjala@....fi, luto@...capital.net,
	mst@...hat.com, cocci@...teme.lip6.fr,
	linux-kernel@...r.kernel.org,
	"Luis R. Rodriguez" <mcgrof@...e.com>,
	Juergen Gross <jgross@...e.com>,
	Daniel Vetter <daniel.vetter@...ll.ch>,
	Dave Airlie <airlied@...hat.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>, x86@...nel.org
Subject: Re: [PATCH v4 2/8] init.h: add __read_mostly to early_param_on_off()

On Wed, Apr 29, 2015 at 02:44:21PM -0700, Luis R. Rodriguez wrote:
> From: "Luis R. Rodriguez" <mcgrof@...e.com>

So this one is missing a commit message too but we need to talk about
this. Why are we adding __read_mostly in the macro? This would put every
param declared this way into __section__(".data..read_mostly") and I'm
not really convinced that is needed.

Those setup params get accessed a couple of times only during boot, in
non-critical paths so we don't really care.

If you care about pat_enabled being read a lot, you could do:

int __read_mostly pat_enabled;

only for it.

But for every param declared this way? I'm not sure we want that...

> Cc: Andy Walls <awalls@...metrocast.net>
> Cc: Doug Ledford <dledford@...hat.com>
> Cc: Andy Lutomirski <luto@...capital.net>
> Cc: Ingo Molnar <mingo@...e.hu>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Juergen Gross <jgross@...e.com>
> Cc: Daniel Vetter <daniel.vetter@...ll.ch>
> Cc: Dave Airlie <airlied@...hat.com>
> Cc: Bjorn Helgaas <bhelgaas@...gle.com>
> Cc: Borislav Petkov <bp@...e.de>
> Cc: Michael S. Tsirkin <mst@...hat.com>
> Cc: linux-kernel@...r.kernel.org
> Cc: x86@...nel.org
> Signed-off-by: Luis R. Rodriguez <mcgrof@...e.com>
> ---
>  include/linux/init.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/linux/init.h b/include/linux/init.h
> index 21b6d76..a0385cc 100644
> --- a/include/linux/init.h
> +++ b/include/linux/init.h
> @@ -272,7 +272,7 @@ struct obs_kernel_param {
>  
>  #define early_param_on_off(str_on, str_off, var, config)		\
>  									\
> -	int var = IS_ENABLED(config);					\
> +	int __read_mostly var = IS_ENABLED(config);			\
>  									\
>  	static int __init parse_##var##_on(char *arg)			\
>  	{								\

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
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