Re: [PATCH] cpuacct: add a branch prediction

From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
To: Li Zefan <lizf@cn.fujitsu.com>
Cc: Ingo Molnar <mingo@elte.hu>,
	Peter Zijlstra <a.p.zijlstra@chello.nl>,
	Paul Menage <menage@google.com>,
	Balbir Singh <balbir@linux.vnet.ibm.com>,
	LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] cpuacct: add a branch prediction
Date: Thu, 26 Feb 2009 17:07:38 +0900	[thread overview]
Message-ID: <20090226170738.a982057b.kamezawa.hiroyu@jp.fujitsu.com> (raw)
In-Reply-To: <49A6475F.4000502@cn.fujitsu.com>

On Thu, 26 Feb 2009 15:40:15 +0800
Li Zefan <lizf@cn.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@cn.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