Messages in this thread Patch in this message | | | From | Claudio Fontana <> | Subject | [RFC] tsacct: fixup ac_pid field to contain tgid | Date | Tue, 5 Mar 2019 13:44:17 +0100 |
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From: Claudio Fontana <claudio.fontana@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.fontana@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
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