linux-kernel - [patch] dubious process system time.

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Date:	Thu, 24 Aug 2006 14:18:25 +0200
From:	Martin Schwidefsky <schwidefsky@...ibm.com>
To:	linux-kernel@...r.kernel.org
Subject: [patch] dubious process system time.

From: Martin Schwidefsky <schwidefsky@...ibm.com>

[patch] dubious process system time.

The system time that is accounted to a process includes the time spent
in three different contexts: normal system time, hardirq time and
softirq time. To account hardirq time and sortirq time to a process
seems wrong, because the process could just happen to run when the
interrupt arrives that was caused by an i/o for a completly different
process. And the sum over stime and cstime of all processes won't
match cputstat->system either. 
The following patch changes the accounting of system time so that
hardirq and softirq time are not accounted to a process anymore.

Signed-off-by: Martin Schwidefsky <schwidefsky@...ibm.com>
---

 kernel/sched.c |    7 +++----
 1 files changed, 3 insertions(+), 4 deletions(-)

diff -urpN linux-2.6/kernel/sched.c linux-2.6-patched/kernel/sched.c
--- linux-2.6/kernel/sched.c	2006-08-01 10:09:55.000000000 +0200
+++ linux-2.6-patched/kernel/sched.c	2006-08-24 13:42:40.000000000 +0200
@@ -2939,17 +2939,16 @@ void account_system_time(struct task_str
 	struct rq *rq = this_rq();
 	cputime64_t tmp;

-	p->stime = cputime_add(p->stime, cputime);
-
 	/* Add system time to cpustat. */
 	tmp = cputime_to_cputime64(cputime);
 	if (hardirq_count() - hardirq_offset)
 		cpustat->irq = cputime64_add(cpustat->irq, tmp);
 	else if (softirq_count())
 		cpustat->softirq = cputime64_add(cpustat->softirq, tmp);
-	else if (p != rq->idle)
+	else if (p != rq->idle) {
+		p->stime = cputime_add(p->stime, cputime);
 		cpustat->system = cputime64_add(cpustat->system, tmp);
-	else if (atomic_read(&rq->nr_iowait) > 0)
+	} else if (atomic_read(&rq->nr_iowait) > 0)
 		cpustat->iowait = cputime64_add(cpustat->iowait, tmp);
 	else
 		cpustat->idle = cputime64_add(cpustat->idle, tmp);
-
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