Messages in this thread | | | Date | Mon, 6 Jul 2015 20:15:29 -0400 | From | Steven Rostedt <> | Subject | Re: [PATCH v2] sched: introduce sched_switch_post trace event |
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On Mon, 6 Jul 2015 12:15:45 -0700 Cong Wang <xiyou.wangcong@gmail.com> wrote:
> Currently we only have one sched_switch trace event > for task switching, which is generated very early during > task switch. When we try to monitor per-container perf > events, this is not what we expect. > > For example, we have a process A which is in the cgroup > we monitor, and process B which isn't, when kernel switches > from B to A, the sched_switch event is not recorded for this > cgroup since it belongs to B (current process is still B > util we finish the switch), but we require this event to > signal that process A in this cgroup gets scheduled. This is > crucial for calculating schedule latency (like `perf sched`).
I just want to understand this correctly. Does perf sched only listen to events that are executed by the task in a particular cgroup? There's no way to say "check sched_switch field next"?
> > Ideally, we need to split the sched_switch event into two: > sched_in event before we perform the switch, and sched_out > event after we perform the switch. However, for compatibility, > we can not change the sched_switch event. So before we have > trace event alias, we can just reuse sched_switch and introduce > sched_switch_post event instead. > > Suggested-by: Steven Rostedt <rostedt@goodmis.org> > Cc: Steven Rostedt <rostedt@goodmis.org> > Cc: Ingo Molnar <mingo@redhat.com> > Cc: Peter Zijlstra <peterz@infradead.org> > Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com> > Signed-off-by: Cong Wang <cwang@twopensource.com> > --- > include/trace/events/sched.h | 43 ++++++++++++++++++++++++++++++++++++++++++- > kernel/sched/core.c | 1 + > 2 files changed, 43 insertions(+), 1 deletion(-) > > diff --git a/include/trace/events/sched.h b/include/trace/events/sched.h > index d57a575..4bc7db5 100644 > --- a/include/trace/events/sched.h > +++ b/include/trace/events/sched.h > @@ -112,7 +112,9 @@ static inline long __trace_sched_switch_state(struct task_struct *p) > #endif /* CREATE_TRACE_POINTS */ > > /* > - * Tracepoint for task switches, performed by the scheduler: > + * Tracepoints for task switches, performed by the scheduler: > + * sched_switch is performed before task switch, > + * sched_switch_post is performed after task switch. > */ > TRACE_EVENT(sched_switch, > > @@ -153,6 +155,45 @@ TRACE_EVENT(sched_switch, > __entry->next_comm, __entry->next_pid, __entry->next_prio) > ); > > +TRACE_EVENT(sched_switch_post, > + > + TP_PROTO(struct task_struct *prev, > + struct task_struct *curr), > + > + TP_ARGS(prev, curr), > + > + TP_STRUCT__entry( > + __array( char, prev_comm, TASK_COMM_LEN ) > + __field( pid_t, prev_pid ) > + __field( int, prev_prio ) > + __field( long, prev_state ) > + __array( char, curr_comm, TASK_COMM_LEN ) > + __field( pid_t, curr_pid ) > + __field( int, curr_prio ) > + ), > + > + TP_fast_assign( > + memcpy(__entry->curr_comm, curr->comm, TASK_COMM_LEN); > + __entry->prev_pid = prev->pid; > + __entry->prev_prio = prev->prio; > + __entry->prev_state = __trace_sched_switch_state(prev); > + memcpy(__entry->prev_comm, prev->comm, TASK_COMM_LEN); > + __entry->curr_pid = curr->pid; > + __entry->curr_prio = curr->prio; > + ), > + > + TP_printk("prev_comm=%s prev_pid=%d prev_prio=%d prev_state=%s%s ==> curr_comm=%s curr_pid=%d curr_prio=%d", > + __entry->prev_comm, __entry->prev_pid, __entry->prev_prio, > + __entry->prev_state & (TASK_STATE_MAX-1) ? > + __print_flags(__entry->prev_state & (TASK_STATE_MAX-1), "|", > + { 1, "S"} , { 2, "D" }, { 4, "T" }, { 8, "t" }, > + { 16, "Z" }, { 32, "X" }, { 64, "x" }, > + { 128, "K" }, { 256, "W" }, { 512, "P" }, > + { 1024, "N" }) : "R", > + __entry->prev_state & TASK_STATE_MAX ? "+" : "", > + __entry->curr_comm, __entry->curr_pid, __entry->curr_prio) > +); > +
This looks identical to trace_sched_switch. Please convert both to a DECLARE_EVENT_CLASS() and DEFINE_EVENT()s.
-- Steve
> /* > * Tracepoint for a task being migrated: > */ > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index 78b4bad10..3c74cf4 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -2490,6 +2490,7 @@ static struct rq *finish_task_switch(struct task_struct *prev) > } > > tick_nohz_task_switch(current); > + trace_sched_switch_post(prev, current); > return rq; > } >
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