[RFC][PATCH 09/10] taskstats: Fix exit CPU time accounting

[Michael Holzheu]

Subject: [PATCH] taskstats: Fix exit CPU time accounting

From: Michael Holzheu <holzheu@xxxxxxxxxxxxxxxxxx>

Currently there are code pathes (e.g. for kthreads) where the consumed
CPU time is not accounted to the parents cumulative counters.
Now CPU time is accounted to the parent, if the exit accounting has not
been done correctly.

Signed-off-by: Michael Holzheu <holzheu@xxxxxxxxxxxxxxxxxx>
---
 include/linux/sched.h |    1 +
 kernel/exit.c         |   35 +++++++++++++++++++++++++++++++++++
 2 files changed, 36 insertions(+)

Index: git-linux-2.6/include/linux/sched.h
===================================================================
--- git-linux-2.6.orig/include/linux/sched.h	2010-09-23 14:16:37.000000000 +0200
+++ git-linux-2.6/include/linux/sched.h	2010-09-23 14:17:20.000000000 +0200
@@ -1282,6 +1282,7 @@
 	cputime_t prev_utime, prev_stime, prev_sttime;
 #endif
 	unsigned long long acct_time;		/* Time for last accounting */
+	int exit_accounting_done;
 	unsigned long nvcsw, nivcsw; /* context switch counts */
 	struct timespec start_time; 		/* monotonic time */
 	struct timespec real_start_time;	/* boot based time */
Index: git-linux-2.6/kernel/exit.c
===================================================================
--- git-linux-2.6.orig/kernel/exit.c	2010-09-23 14:16:37.000000000 +0200
+++ git-linux-2.6/kernel/exit.c	2010-09-23 14:17:20.000000000 +0200
@@ -157,11 +157,45 @@
 	put_task_struct(tsk);
 }
 
+static void account_to_parent(struct task_struct *p)
+{
+	struct signal_struct *psig, *sig;
+	struct task_struct *tsk_parent;
+
+	read_lock(&tasklist_lock);
+	tsk_parent = p->real_parent;
+	if (!tsk_parent) {
+		read_unlock(&tasklist_lock);
+		return;
+	}
+	get_task_struct(tsk_parent);
+	read_unlock(&tasklist_lock);
+
+	// printk("XXX Fix accounting: pid=%d ppid=%d\n", p->pid, tsk_parent->pid);
+	spin_lock_irq(&tsk_parent->sighand->siglock);
+	psig = tsk_parent->signal;
+	sig = p->signal;
+	psig->cutime = cputime_add(psig->cutime,
+				   cputime_add(sig->cutime, p->utime));
+	psig->cstime = cputime_add(psig->cstime,
+				   cputime_add(sig->cstime, p->stime));
+	psig->csttime = cputime_add(psig->csttime,
+				    cputime_add(sig->csttime, p->sttime));
+	psig->cgtime = cputime_add(psig->cgtime,
+		       cputime_add(p->gtime,
+		       cputime_add(sig->gtime, sig->cgtime)));
+	p->exit_accounting_done = 1;
+	spin_unlock_irq(&tsk_parent->sighand->siglock);
+	put_task_struct(tsk_parent);
+}
 
 void release_task(struct task_struct * p)
 {
 	struct task_struct *leader;
 	int zap_leader;
+
+	if (!p->exit_accounting_done)
+		account_to_parent(p);
 repeat:
 	tracehook_prepare_release_task(p);
 	/* don't need to get the RCU readlock here - the process is dead and
@@ -1279,6 +1313,7 @@
 			psig->cmaxrss = maxrss;
 		task_io_accounting_add(&psig->ioac, &p->ioac);
 		task_io_accounting_add(&psig->ioac, &sig->ioac);
+		p->exit_accounting_done = 1;
 		spin_unlock_irq(&p->real_parent->sighand->siglock);
 	}
 


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