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

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Message-ID: <20090226083702.GI11421@balbir.in.ibm.com>
Date:	Thu, 26 Feb 2009 14:07:02 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.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>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] cpuacct: add a branch prediction

* Li Zefan <lizf@...fujitsu.com> [2009-02-26 15:40:15]:

> 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))

What happens if most distros make cpuacct_subsys active? Can we decide
on unlikely depending on how the system is configured?


-- 
	Balbir
--
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