linux-kernel - [PATCH] fix granularity of task

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Date:	Thu, 12 Nov 2009 13:33:45 +0900
From:	Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>
To:	Stanislaw Gruszka <sgruszka@...hat.com>
CC:	Américo Wang <xiyou.wangcong@...il.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: [PATCH] fix granularity of task_u/stime(), v2

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@...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@...fujitsu.com>
---
 kernel/sched.c |   22 +++++++++++++---------
 1 files changed, 13 insertions(+), 9 deletions(-)

diff --git a/kernel/sched.c b/kernel/sched.c
index 3c11ae0..1f8d028 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -5172,41 +5172,45 @@ 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;
 }
-- 
1.6.5.2


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