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

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Message-Id: <200708310302.l7V32ZpV410222@sabah.engr.sgi.com>
Date:	Thu, 30 Aug 2007 20:02:35 -0700 (PDT)
From:	Jonathan Lim <jlim@....com>
To:	balbir@...ux.vnet.ibm.com
Cc:	guichaz@...oo.fr (Guillaume Chazarain),
	akpm@...ux-foundation.org (Andrew Morton),
	linux-kernel@...r.kernel.org (Linux Kernel Mailing List),
	jlan@...ulhu.engr.sgi.com (Jay Lan)
Subject: Re: [PATCH] Add all thread stats for TASKSTATS_CMD_ATTR_TGID

On Sat Aug 25 21:58:44 2007, balbir@...ux.vnet.ibm.com wrote:
> 
> > 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).

In CSA 3.0 ...

csa_acct_eop(int exitcode, struct task_struct *p)

        csa->ac_btime = boottime +
                        ((p->start_time.tv_nsec < NSEC_PER_SEC/2) ?
                         p->start_time.tv_sec :
                         p->start_time.tv_sec +1);

where 

        do_posix_clock_monotonic_gettime(&uptime);
        boottime = xtime.tv_sec - uptime.tv_sec;

In an upcoming version of CSA ...

csa_acct_eop(struct taskstats *p)

        csa->ac_btime = p->ac_btime;

where

        do_posix_clock_monotonic_gettime(&uptime);
        ts = uptime - tsk->start_time;
        p->ac_btime = get_seconds() - ts.tv_sec;
                    = xtime.tv_sec - (uptime - tsk->start_time);
                    = (xtime.tv_sec - uptime) + tsk->start_time;

So they're basically equivalent.

Jonathan
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