Re: [PATCH] taskstats: fix sub-threads accounting

Shailabh Nagar
2006-10-31T03:03:09Z

Oleg Nesterov wrote:
> If there are no listeners, taskstats_exit_send() just returns because
> taskstats_exit_alloc() didn't allocate *tidstats. This is wrong, each
> sub-thread should do fill_tgid_exit() on exit, otherwise its ->delays
> is not recorded in ->signal->stats and lost.

Good catch. Thanks for the detailed look at the delay accounting code.

>
> Q: We don't send TASKSTATS_TYPE_AGGR_TGID when single-threaded process
> exits. Is it good? How can the listener figure out that it was actually
> a process exit, not sub-thread?

We had a detailed discussion on this on lkml earlier. The overhead of
sending essentially the same data twice (once as AGGR_TGID and once as
PID) was deemed too heavy esp. as the taskstats structure size grew.
Also, single threaded exit is a common case.

Using process events, its possible for user space to distinguish single
threaded process exits.

>
> Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>

Acked-by: Shailabh Nagar <nagar@watson.ibm.com>

>
> --- STATS/kernel/taskstats.c~2_send 2006-10-30 23:47:46.000000000 +0300
> +++ STATS/kernel/taskstats.c 2006-10-31 00:14:42.000000000 +0300
> @@ -446,10 +446,9 @@ void taskstats_exit_send(struct task_str
> int is_thread_group;
> struct nlattr *na;
>
> - if (!family_registered || !tidstats)
> + if (!family_registered)
> return;
>
> - rc = 0;
> /*
> * Size includes space for nested attributes
> */
> @@ -457,8 +456,15 @@ void taskstats_exit_send(struct task_str
> nla_total_size(sizeof(struct taskstats)) + nla_total_size(0);
>
> is_thread_group = (tsk->signal->stats != NULL);
> - if (is_thread_group)
> - size = 2 * size; /* PID + STATS + TGID + STATS */
> + if (is_thread_group) {
> + /* PID + STATS + TGID + STATS */
> + size = 2 * size;
> + /* fill the tsk->signal->stats structure */
> + fill_tgid_exit(tsk);
> + }
> +
> + if (!tidstats)
> + return;
>
> rc = prepare_reply(NULL, TASKSTATS_CMD_NEW, &rep_skb, &reply, size);
> if (rc < 0)
> @@ -478,11 +484,8 @@ void taskstats_exit_send(struct task_str
> goto send;
>
> /*
> - * tsk has/had a thread group so fill the tsk->signal->stats structure
> * Doesn't matter if tsk is the leader or the last group member leaving
> */
> -
> - fill_tgid_exit(tsk);
> if (!group_dead)
> goto send;
>
>