On Fri Aug 31 00:24:47 2007, [email protected] wrote:
>
> Jonathan Lim wrote:
> > On Sat Aug 25 21:58:44 2007, [email protected] 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.
>
> Excellent, so can Guillaume change ac_btime to be just tsk->start_time?
I don't think so. Current time (xtime) is relative to the epoch; uptime and
tsk->start_time (jiffies) are both relative to some boot time. So you need to
subtract uptime from xtime to get the boot time relative to the epoch, then add
tsk->start_time. The result is what ac_btime should be set to.
I think his recent changes are as follows:
--- a/kernel/tsacct.c Fri Aug 31 01:42:23 2007 -0700
+++ b/kernel/tsacct.c Tue Aug 28 20:35:27 2007 +0200
...
-void bacct_add_tsk(struct taskstats *stats, struct task_struct *tsk)
+static void fill_wall_times(struct taskstats *stats, struct task_struct *task)
...
- ts = timespec_sub(uptime, tsk->start_time);
+ ts = timespec_sub(uptime, task->start_time);
...
- stats->ac_btime = get_seconds() - ts.tv_sec;
...
+ stats->ac_btime = get_seconds() - ts.tv_sec;
So really no different from before, which is correct.
Jonathan
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