linux-kernel - Re: [PATCH] cpuacct: add a branch prediction

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Message-Id: <20090226170738.a982057b.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Thu, 26 Feb 2009 17:07:38 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Li Zefan <lizf@...fujitsu.com>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Menage <menage@...gle.com>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] cpuacct: add a branch prediction

On Thu, 26 Feb 2009 15:40:15 +0800
Li Zefan <lizf@...fujitsu.com> wrote:

> cpuacct_charge() is in fast-path, and checking of !cpuacct_susys.active
> always returns false after cpuacct has been initialized at system boot.
> 
> Signed-off-by: Li Zefan <lizf@...fujitsu.com>
> ---
>  kernel/sched.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/kernel/sched.c b/kernel/sched.c
> index 410eec4..fd2f7fc 100644
> --- a/kernel/sched.c
> +++ b/kernel/sched.c
> @@ -9589,7 +9589,7 @@ static void cpuacct_charge(struct task_struct *tsk, u64 cputime)
>  	struct cpuacct *ca;
>  	int cpu;
>  
> -	if (!cpuacct_subsys.active)
> +	if (unlikely(!cpuacct_subsys.active))
>  		return;
>  
(Just curious)
I wonder "ca = task_ca(tsk)" will return NULL if cpuacct subsys is not initalized.
Then, can we just remove this check ?


Thanks,
-Kame

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