Subject: Re: [PATCH] fix granularity of task_u/stime(), v2
From: Peter Zijlstra <peterz@infradead.org>
To: Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>
Cc: Stanislaw Gruszka <sgruszka@redhat.com>,
       =?ISO-8859-1?Q?Am=E9rico?= Wang <xiyou.wangcong@gmail.com>,
       Spencer Candland <spencer@bluehost.com>, linux-kernel@vger.kernel.org,
       Ingo Molnar <mingo@elte.hu>, Oleg Nesterov <oleg@redhat.com>
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Date: Thu, 12 Nov 2009 15:15:58 +0100
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On Thu, 2009-11-12 at 13:33 +0900, Hidetoshi Seto wrote:
> Originally task_s/utime() were designed to return clock_t but later
> changed to return cputime_t by following commit:
> 
>   commit efe567fc8281661524ffa75477a7c4ca9b466c63
>   Author: Christian Borntraeger <borntraeger@de.ibm.com>
>   Date:   Thu Aug 23 15:18:02 2007 +0200
> 
> It only changed the type of return value, but not the implementation.
> As the result the granularity of task_s/utime() is still that of
> clock_t, not that of cputime_t.
> 
> So using task_s/utime() in __exit_signal() makes values accumulated
> to the signal struct to be rounded and coarse grained.
> 
> This patch removes casts to clock_t in task_u/stime(), to keep
> granularity of cputime_t over the calculation.
> 
> v2:
>   Use div_u64() to avoid error "undefined reference to `__udivdi3`"
>   on some 32bit systems.
> 
> Signed-off-by: Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>

/me hates all the cputime_t and clock_t mess.. but I guess the patch is
good.

Thanks.


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