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

[Balbir Singh <balbir@linux.vnet.ibm.com>]

* Michael Holzheu <holzheu@linux.vnet.ibm.com> [2010-09-23 16:02:21]:

> Subject: [PATCH] taskstats: Fix exit CPU time accounting
> 
> From: Michael Holzheu <holzheu@linux.vnet.ibm.com>
> 
> 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.
>

Does this impact account of the init process? Why do we care about
accounting the time to the parent? In the case of tgid, all threads
data makes sense. What is the benefit or gap we are trying to address
in terms of lost data or accountability?
 
> Signed-off-by: Michael Holzheu <holzheu@linux.vnet.ibm.com>
> ---
>  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);
>  	}
> 
> 
> 

-- 
	Three Cheers,
	Balbir