linux-kernel - Re: [PATCH tip/sched/core] introduce task_times() to replace task

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Message-ID: <4B0B8683.6020104@jp.fujitsu.com>
Date:	Tue, 24 Nov 2009 16:08:51 +0900
From:	Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>
To:	Stanislaw Gruszka <sgruszka@...hat.com>
CC:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>,
	Spencer Candland <spencer@...ehost.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Balbir Singh <balbir@...ibm.com>,
	Américo Wang <xiyou.wangcong@...il.com>
Subject: Re: [PATCH tip/sched/core] introduce task_times() to replace	task_[us]time()
 pair

Hidetoshi Seto wrote:
> And just now I noticed that using msecs_to_cputime() is problematic,
> since the type of its return value is "unsigned long" so not 64bit.
> I'll make and post a patch to fix this asap.

Sorry, I was confused.  Please ignore the above.

The problem is that since the type of msecs_to_cputime() argument is
unsigned int, it would be wrong if calculated msecs is greater than
UINT_MAX.

Another problem is that msecs_to_jiffies() returns MAX_JIFFY_OFFSET
if msecs > INT_MAX. 

   5168 #ifndef nsecs_to_cputime
   5169 # define nsecs_to_cputime(__nsecs) \
   5170         msecs_to_cputime(div_u64((__nsecs), NSEC_PER_MSEC))
   5171 #endif

    452 unsigned long msecs_to_jiffies(const unsigned int m)
    453 {
    454         /*
    455          * Negative value, means infinite timeout:
    456          */
    457         if ((int)m < 0)
    458                 return MAX_JIFFY_OFFSET;
     :

What I need here is a simple function can convert 64bit nsecs to
cputime_t, which is unsigned long in asm-generic/cputime.h.
Humm...


Thanks,
H.Seto

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