From: Claudio Fontana <claudio.font...@gmail.com>
commit f3cef7a99469 ("[PATCH] csa: basic accounting over taskstats")
introduced accounting fields over taskstats,
however the ac_pid field has been filled in with the Linux pid
(the tid), instead of the POSIX pid (the tgid) like for acct.c
This change aligns the ac_pid field in tsacct with
the ac_pid field in acct.c
Signed-off-by: Claudio Fontana <claudio.font...@gmail.com>
---
kernel/tsacct.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
Hello all,
this is just to spark some responses regarding the current status
of tsacct field ac_pid, which currently is filled up with pid,
where I would expect a tgid, like for acct.c.
in acct.c:
ac.ac_pid = task_tgid_nr_ns(current, ns);
in tsacct.c:
stats->ac_pid = task_pid_nr_ns(tsk, pid_ns);
I am trying to have a low overhead way from a C userspace program
to get the tgid given a single pid.
I have tried using the tgid map provided by ftrace, however
parsing and reparsing the text of the whole map is quite expensive.
Reading from /proc/PID/ is of higher overhead, with multiple opens,
reads and close calls necessary.
I have experimented with previous work by Andrey Vagin on
task_diag (the old and the new method), but neither is currently
upstream; one of the comments at the time mentioned that the
functionality should instead be merged into netlink taskstats.
https://criu.org/Task-diag
https://lwn.net/Articles/683371/
I think that for backward compatibility reasons, this particular
change in this RFC cannot be applied as such.
Maybe adding a new field ac_tgid would be preferable?
Maybe the information could be carried inside the NETLINK
taskstat response as an unconditional additional
TASKSTATS_TYPE_TGID field, even when the TASKSTATS_CMD_GET
requests a TASKSTATS_CMD_ATTR_PID?
Thank you and looking forward for your comments,
Claudio
diff --git a/kernel/tsacct.c b/kernel/tsacct.c
index 370724b..28ecedb 100644
--- a/kernel/tsacct.c
+++ b/kernel/tsacct.c
@@ -59,7 +59,7 @@ void bacct_add_tsk(struct user_namespace *user_ns,
stats->ac_flag |= AXSIG;
stats->ac_nice = task_nice(tsk);
stats->ac_sched = tsk->policy;
- stats->ac_pid = task_pid_nr_ns(tsk, pid_ns);
+ stats->ac_pid = task_tgid_nr_ns(tsk, pid_ns);
rcu_read_lock();
tcred = __task_cred(tsk);
stats->ac_uid = from_kuid_munged(user_ns, tcred->uid);
--
2.7.4
