From: Li Zefan <lizf@cn.fujitsu.com>
To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.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 16:35:33 +0800 [thread overview]
Message-ID: <49A65455.4030204@cn.fujitsu.com> (raw)
In-Reply-To: <20090226172234.a931931f.kamezawa.hiroyu@jp.fujitsu.com>
KAMEZAWA Hiroyuki wrote:
> On Thu, 26 Feb 2009 16:17:31 +0800
> Li Zefan <lizf@cn.fujitsu.com> wrote:
>
>> 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.
>>
> My point is,
>
Ah, I see.
> ca = task_ca(tsk)
> for (; ca; ca->parent) {
> ...
> }
>
ca is not checked before hierarchy support, and it's a side-effect.
Before cpuacct is initialized, css == task->cgroups->subsys[cpuacct_subsys] == NULL,
but ca = task_ca(tsk) is not necessarily NULL, unless struct cgroup_subsys_state is the
first member of struct cpuacct.
And the above code actually should be:
do {
...
} while (ca->parent);
> What is problem even if ca is NULL.
>
next prev parent reply other threads:[~2009-02-26 8:35 UTC|newest]
Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-02-26 7:40 [PATCH] cpuacct: add a branch prediction Li Zefan
2009-02-26 8:07 ` KAMEZAWA Hiroyuki
2009-02-26 8:17 ` Li Zefan
2009-02-26 8:22 ` KAMEZAWA Hiroyuki
2009-02-26 8:35 ` Li Zefan [this message]
2009-02-26 8:40 ` KAMEZAWA Hiroyuki
2009-02-26 10:10 ` Bharata B Rao
2009-02-26 10:28 ` KAMEZAWA Hiroyuki
2009-02-26 10:44 ` Peter Zijlstra
2009-02-26 10:55 ` KAMEZAWA Hiroyuki
2009-02-26 11:22 ` Peter Zijlstra
2009-02-26 11:17 ` KAMEZAWA Hiroyuki
2009-02-26 11:28 ` Peter Zijlstra
2009-02-26 12:06 ` KAMEZAWA Hiroyuki
2009-02-26 12:20 ` Peter Zijlstra
2009-02-26 12:26 ` Ingo Molnar
2009-02-26 12:40 ` Arnd Bergmann
2009-02-27 4:25 ` Paul Mackerras
2009-02-26 16:45 ` Paul E. McKenney
2009-02-27 0:58 ` KAMEZAWA Hiroyuki
2009-02-27 1:29 ` Paul E. McKenney
2009-02-27 3:22 ` [RFC][PATCH] remove rq->lock from cpuacct cgroup (Was " KAMEZAWA Hiroyuki
2009-03-02 14:56 ` Peter Zijlstra
2009-03-02 23:42 ` KAMEZAWA Hiroyuki
2009-03-03 7:51 ` Peter Zijlstra
2009-03-03 9:04 ` KAMEZAWA Hiroyuki
2009-03-03 9:40 ` Peter Zijlstra
2009-03-03 10:42 ` KAMEZAWA Hiroyuki
2009-03-03 10:44 ` KAMEZAWA Hiroyuki
2009-03-03 11:54 ` Peter Zijlstra
2009-03-04 6:32 ` [PATCH] remove rq->lock from cpuacct cgroup v2 KAMEZAWA Hiroyuki
2009-03-04 7:54 ` Bharata B Rao
2009-03-04 8:20 ` KAMEZAWA Hiroyuki
2009-03-04 8:46 ` KAMEZAWA Hiroyuki
2009-03-04 10:35 ` Bharata B Rao
2009-03-04 12:11 ` Bharata B Rao
2009-03-04 14:17 ` KAMEZAWA Hiroyuki
2009-02-26 8:37 ` [PATCH] cpuacct: add a branch prediction Balbir Singh
2009-02-26 8:41 ` Li Zefan
2009-02-26 10:40 ` Balbir Singh
2009-02-26 10:43 ` Peter Zijlstra
2009-02-26 8:43 ` KAMEZAWA Hiroyuki
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