On Mon, 6 Jul 2015 12:15:45 -0700
Cong Wang <xiyou.wangc...@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 <rost...@goodmis.org>
> Cc: Steven Rostedt <rost...@goodmis.org>
> Cc: Ingo Molnar <mi...@redhat.com>
> Cc: Peter Zijlstra <pet...@infradead.org>
> Signed-off-by: Cong Wang <xiyou.wangc...@gmail.com>
> Signed-off-by: Cong Wang <cw...@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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