linux-kernel - Re: [PATCH] Add all thread stats for TASKSTATS_CMD_ATTR

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Message-ID: <46D10884.6040401@linux.vnet.ibm.com>
Date:	Sun, 26 Aug 2007 10:28:44 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	Guillaume Chazarain <guichaz@...oo.fr>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Jay Lan <jlan@...r.sgi.com>, Jonathan Lim <jlim@....com>
Subject: Re: [PATCH] Add all thread stats for TASKSTATS_CMD_ATTR_TGID

Guillaume Chazarain wrote:
> Le Mon, 20 Aug 2007 22:31:08 +0530,
> Balbir Singh <balbir@...ux.vnet.ibm.com> a écrit :
> 
>>> --- a/kernel/taskstats.c	Sat Aug 18 17:15:17 2007 -0700
>>> +++ b/kernel/taskstats.c	Sun Aug 19 17:20:15 2007 +0200
>>> @@ -246,6 +246,8 @@ static int fill_tgid(pid_t tgid, struct 
>>>
>>>  		stats->nvcsw += tsk->nvcsw;
>>>  		stats->nivcsw += tsk->nivcsw;
>>> +		bacct_add_tsk(stats, tsk);
>>> +		xacct_add_tsk(stats, tsk);
>> I'm afraid this is still not good enough. bacct_add_tsk() will assign
>> values and do nothing in the loop (HINT: no summation).
> 
> Hi Balbir, thank you for your review. I agree with everything you said
> and am on my way to do it as time permits, but I have some trouble
> understanding this part. You stated that bacct_add_tsk() would overwrite
> the stats of each thread in the tgid stats, but the other part of the
> patch is the (actually wrong) combination of stats in xxx_add_tsk()
> using min/max/sum.
> 

Hi, Guillaume,

The CSA code was written by Jay Lan, but I'll see if I can answer your
questions. In the current implementation, CSA does not use TGID exit
notifications. In fill_pid(), both bacct_add_tsk() and xacct_add_tsk()
are called (which is correct), they complement each other.

The code needs refactoring to ensure that they can work together
in the fill_tgid() scenario.

> Also, I don't understand why the code to update btime:
> 
>         /* calculate task elapsed time in timespec */
>         do_posix_clock_monotonic_gettime(&uptime);
>         ts = timespec_sub(uptime, tsk->start_time);
> 	...
>         stats->ac_btime = get_seconds() - ts.tv_sec;
> 
> does not simply use tsk->start_time or tsk->real_start_time without
> comparing it to the current time.
> 

>From what I understand, task->start_time and task->real_start_time
are taken from the realtime clock. The accounting in CSA seems
to be very similar to the accounting done in do_acct_process()
(kernel/acct.c).

Jay/Jonathan any comments?


-- 
	Warm Regards,
	Balbir Singh
	Linux Technology Center
	IBM, ISTL
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