Subject: Re: [updated] [Patch 6/8] delay accounting usage of taskstats
	interface
From: Thomas Gleixner <tglx@linutronix.de>
To: balbir@in.ibm.com
Cc: linux-kernel@vger.kernel.org, lse-tech@lists.sourceforge.net,
       jlan@engr.sgi.com, akpm@osdl.org
In-Reply-To: <20060504184442.GC6966@in.ibm.com>
References: <20060502061930.GC22607@in.ibm.com>
	 <20060504184442.GC6966@in.ibm.com>
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Date: Tue, 09 May 2006 11:46:48 +0000
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On Fri, 2006-05-05 at 00:14 +0530, Balbir Singh wrote:

>  #else
>  static inline void delayacct_set_flag(int flag)
>  {}

Please make this

static inline void delayacct_set_flag(int flag) { }

Same in all other files

> @@ -89,6 +99,9 @@ static inline void delayacct_blkio_start
>  {}
>  static inline void delayacct_blkio_end(void)
>  {}
> +static inline int delayacct_add_tsk(struct taskstats *d,
> +					struct task_struct *tsk)
> +{ return 0; }

{
	return 0;
}

> +	 *
> +	 * xxx_count is the number of delay values recorded
> +	 * xxx_delay_total is the corresponding cumulative delay in nanoseconds
> +	 *
> +	 * xxx_delay_total wraps around to zero on overflow
> +	 * xxx_count incremented regardless of overflow
> +	 */

Please use a structure for that.

struct delay_account {
	ktime_t delay;
	u64 count;
};

Also instead of having tons of fields added, please use something like

enum {
	CPU_ACCT,
	BLKIO_ACCT,
	....,
	MAX_ACCT_TYPES
};
	struct delay_account stats[MAX_ACCT_TYPES];


> +	/* Delay waiting for cpu, while runnable
> +	 * count, delay_total NOT updated atomically
> +	 */
> +	__u64	cpu_count;
> +	__u64	cpu_delay_total;
> +	/* Following four fields atomically updated using task->delays->lock */
> +
> +	/* Delay waiting for synchronous block I/O to complete
> +	 * does not account for delays in I/O submission
> +	 */
> +	__u64	blkio_count;
> +	__u64	blkio_delay_total;
> +
> +	/* Delay waiting for page fault I/O (swap in only) */
> +	__u64	swapin_count;
> +	__u64	swapin_delay_total;
> +
> +	/* cpu "wall-clock" running time
> +	 * On some architectures, value will adjust for cpu time stolen
> +	 * from the kernel in involuntary waits due to virtualization.
> +	 * Value is cumulative, in nanoseconds, without a corresponding count
> +	 * and wraps around to zero silently on overflow

When will this overflow happen ? 2^64 nsec ~= 584 years


> +int __delayacct_add_tsk(struct taskstats *d, struct task_struct *tsk)
> +{

Please add some comment what this code does.

> +	s64 tmp;
> +	struct timespec ts;
> +	unsigned long t1,t2,t3;
> +
> +	tmp = (s64)d->cpu_run_real_total;
> +	tmp += (u64)(tsk->utime + tsk->stime) * TICK_NSEC;
> +	d->cpu_run_real_total = (tmp < (s64)d->cpu_run_real_total) ? 0 : tmp;
> +
> +	/*
> +	 * No locking available for sched_info (and too expensive to add one)
> +	 * Mitigate by taking snapshot of values
> +	 */
> +	t1 = tsk->sched_info.pcnt;
> +	t2 = tsk->sched_info.run_delay;
> +	t3 = tsk->sched_info.cpu_time;
> +
> +	d->cpu_count += t1;
> +
> +	jiffies_to_timespec(t2, &ts);
> +	tmp = (s64)d->cpu_delay_total + timespec_to_ns(&ts);
> +	d->cpu_delay_total = (tmp < (s64)d->cpu_delay_total) ? 0 : tmp;
> +
> +	tmp = (s64)d->cpu_run_virtual_total + (s64)jiffies_to_usecs(t3) * 1000;
> +	d->cpu_run_virtual_total =
> +		(tmp < (s64)d->cpu_run_virtual_total) ?	0 : tmp;
> +
> +	/* zero XXX_total, non-zero XXX_count implies XXX stat overflowed */
> +
> +	spin_lock(&tsk->delays->lock);
> +	tmp = d->blkio_delay_total + tsk->delays->blkio_delay;
> +	d->blkio_delay_total = (tmp < d->blkio_delay_total) ? 0 : tmp;

I really do not get whatfor all these comparisons are. How can those
values get > 2^63 within a reasonable timeframe ?

> +	tmp = d->swapin_delay_total + tsk->delays->swapin_delay;
> +	d->swapin_delay_total = (tmp < d->swapin_delay_total) ? 0 : tmp;
> +	d->blkio_count += tsk->delays->blkio_count;
> +	d->swapin_count += tsk->delays->swapin_count;
> +	spin_unlock(&tsk->delays->lock);
> +	return 0;
> +}
> diff -puN kernel/taskstats.c~delayacct-taskstats kernel/taskstats.c
> --- linux-2.6.17-rc3/kernel/taskstats.c~delayacct-taskstats	2006-05-04 09:31:59.000000000 +0530
> +++ linux-2.6.17-rc3-balbir/kernel/taskstats.c	2006-05-04 11:27:53.000000000 +0530
> @@ -18,6 +18,7 @@
>  
>  #include <linux/kernel.h>
>  #include <linux/taskstats_kern.h>
> +#include <linux/delayacct.h>
>  #include <net/genetlink.h>
>  #include <asm/atomic.h>
>  
> @@ -120,7 +121,10 @@ static int fill_pid(pid_t pid, struct ta
>  	 *		goto err;
>  	 */
>  
> -err:
> +	rc = delayacct_add_tsk(stats, tsk);
> +	stats->version = TASKSTATS_VERSION;
> +
> +	/* Define err: label here if needed */

Please remove that comment. The err label goes to a place where it makes
sense.

>  	put_task_struct(tsk);
>  	return rc;
>  
> @@ -152,8 +156,14 @@ static int fill_tgid(pid_t tgid, struct 
>  		 *		break;
>  		 */
>  
> +		rc = delayacct_add_tsk(stats, tsk);
> +		if (rc)
> +			break;
> +
>  	} while_each_thread(first, tsk);
>  	read_unlock(&tasklist_lock);
> +	stats->version = TASKSTATS_VERSION;
> +
>  
>  	/*
>  	 * Accounting subsytems can also add calls here if they don't
> _
> -
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