linux-kernel - Re: [PATCH] jump_label: unlikely(x)

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Date:	Fri, 11 Oct 2013 13:57:04 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Roel Kluin <roel.kluin@...il.com>
Cc:	Andrew Jones <drjones@...hat.com>,
	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	"H. Peter Anvin" <hpa@...ux.intel.com>,
	Ingo Molnar <mingo@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] jump_label: unlikely(x) > 0

On Fri, 11 Oct 2013 22:50:50 +0200 (CEST) Roel Kluin <roel.kluin@...il.com> wrote:

> untested, but wasn't this intended instead?
> --------------
> if (unlikely(x) > 0) doesn't seem to help branch prediction
> 
> ...
>
> --- a/include/linux/jump_label.h
> +++ b/include/linux/jump_label.h
> @@ -132,14 +132,14 @@ static __always_inline void jump_label_init(void)
>  
>  static __always_inline bool static_key_false(struct static_key *key)
>  {
> -	if (unlikely(atomic_read(&key->enabled)) > 0)
> +	if (unlikely(atomic_read(&key->enabled) > 0))
>  		return true;
>  	return false;
>  }
>  
>  static __always_inline bool static_key_true(struct static_key *key)
>  {
> -	if (likely(atomic_read(&key->enabled)) > 0)
> +	if (likely(atomic_read(&key->enabled) > 0))
>  		return true;
>  	return false;
>  }

I'm sure this was intended instead ;) The patch doesn't seem to make
any difference in code generation with my gcc.

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