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Commit 761b1d26 authored by Hidetoshi Seto's avatar Hidetoshi Seto Committed by Ingo Molnar
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sched: Fix granularity of task_u/stime() 



Originally task_s/utime() were designed to return clock_t but
later changed to return cputime_t by following commit:

  commit efe567fc
  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: default avatarHidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>
Acked-by: default avatarPeter Zijlstra <peterz@infradead.org>
Cc: xiyou.wangcong@gmail.com
Cc: Spencer Candland <spencer@bluehost.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Stanislaw Gruszka <sgruszka@redhat.com>
LKML-Reference: <4AFB9029.9000208@jp.fujitsu.com>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent ffd44db5

kernel/sched.c

+13 −9
Original line number Diff line number Diff line
@@ -5156,41 +5156,45 @@ cputime_t task_stime(struct task_struct *p) 
	return p->stime;

}

#else



#ifndef nsecs_to_cputime

# define nsecs_to_cputime(__nsecs) \

	msecs_to_cputime(div_u64((__nsecs), NSEC_PER_MSEC))

#endif



cputime_t task_utime(struct task_struct *p)

{

	clock_t utime = cputime_to_clock_t(p->utime),

		total = utime + cputime_to_clock_t(p->stime);

	cputime_t utime = p->utime, total = utime + p->stime;

	u64 temp;



	/*

	 * Use CFS's precise accounting:

	 */

	temp = (u64)nsec_to_clock_t(p->se.sum_exec_runtime);

	temp = (u64)nsecs_to_cputime(p->se.sum_exec_runtime);



	if (total) {

		temp *= utime;

		do_div(temp, total);

	}

	utime = (clock_t)temp;

	utime = (cputime_t)temp;



	p->prev_utime = max(p->prev_utime, clock_t_to_cputime(utime));

	p->prev_utime = max(p->prev_utime, utime);

	return p->prev_utime;

}



cputime_t task_stime(struct task_struct *p)

{

	clock_t stime;

	cputime_t stime;



	/*

	 * Use CFS's precise accounting. (we subtract utime from

	 * the total, to make sure the total observed by userspace

	 * grows monotonically - apps rely on that):

	 */

	stime = nsec_to_clock_t(p->se.sum_exec_runtime) -

			cputime_to_clock_t(task_utime(p));

	stime = nsecs_to_cputime(p->se.sum_exec_runtime) - task_utime(p);



	if (stime >= 0)

		p->prev_stime = max(p->prev_stime, clock_t_to_cputime(stime));

		p->prev_stime = max(p->prev_stime, stime);



	return p->prev_stime;

}