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SubjectRe: [PATCH] cpuacct: add a branch prediction
KAMEZAWA Hiroyuki wrote:
> 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.

Yes, it will be NULL, and that's why we need this check.

> Then, can we just remove this check ?
>

cpuacct_charge() can be called before cpuacct is initialized, so we have to check this
case here.


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