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

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Message-ID: <4AFB8C21.6080404@jp.fujitsu.com>
Date:	Thu, 12 Nov 2009 13:16:33 +0900
From:	Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>
To:	Américo Wang <xiyou.wangcong@...il.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()

Américo Wang wrote:
>>>> 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

>> 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. ;)

Thank you for the information.

According to the following commit which I found that is against "__udivdi3"
error, use of div_u64() will fix this problem, right?

 commit 956dba3caaf66b84fe5f6180e0e4dd03902c7980
 Author: Andy Whitcroft <apw@...onical.com>
 Date:   Wed Jul 1 15:20:59 2009 +0100

I'm now testing modified patch...


Thanks,
H.Seto

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