linux-kernel - Re: [PATCH] fix granularity of task

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Date:	Thu, 12 Nov 2009 10:55:38 +0800
From:	Américo Wang <xiyou.wangcong@...il.com>
To:	Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>
Cc:	Stanislaw Gruszka <sgruszka@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Spencer Candland <spencer@...ehost.com>,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Oleg Nesterov <oleg@...hat.com>
Subject: Re: [PATCH] fix granularity of task_u/stime()

On Thu, Nov 12, 2009 at 10:49 AM, Hidetoshi Seto
<seto.hidetoshi@...fujitsu.com> wrote:
> Hidetoshi Seto wrote:
>> Stanislaw Gruszka wrote:
>>> On Tue, Nov 10, 2009 at 02:47:34PM +0900, Hidetoshi Seto wrote:
>>>> Remove casting to clock_t from task_u/stime(), and keep granularity of
>>>> cputime_t over the calculation.
>>>>
>>>> Signed-off-by: Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>
>>>> ---
>>>>  kernel/sched.c |   21 ++++++++++++---------
>>>>  1 files changed, 12 insertions(+), 9 deletions(-)
>>>>
>>>> diff --git a/kernel/sched.c b/kernel/sched.c
>>>> index 28dd4f4..1632e82 100644
>>>> --- a/kernel/sched.c
>>>> +++ b/kernel/sched.c
>>>> @@ -5171,41 +5171,44 @@ cputime_t task_stime(struct task_struct *p)
>>>>     return p->stime;
>>>>  }
>>>>  #else
>>>> +
>>>> +#ifndef nsecs_to_cputime
>>>> +# define nsecs_to_cputime(__nsecs) msecs_to_cputime((__nsecs) / NSEC_PER_MSEC)
>>>> +#endif
>>>> +
>>> I would like to test, but unfortunately with the patch kernel not build
>>> on my system:
>>>
>>> kernel/built-in.o: In function `task_utime':
>>> /usr/src/rhel5/linux-2.6/kernel/sched.c:5187: undefined reference to
>>> `__udivdi3'
>>> kernel/built-in.o: In function `task_stime':
>>> /usr/src/rhel5/linux-2.6/kernel/sched.c:5208: undefined reference to
>>> `__udivdi3'
>>> make: *** [.tmp_vmlinux1] Error 1
>>
>> Wow, what arch?
>> Could you provide your .config?
>
> Oh, I found I can hit this error on x86_32 (but not on x86_64).
> Maybe something on dividing u64...
>
> I'll try to find fix/workaround for this, but would appreciate if someone
> could tell me what is happening here.

Yeah, this is because on 32-bit gcc tries to use libgcc to do 64-bit
integer computing. You can insert inline asm to force gcc not to
optimize this code. ;)
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