linux-kernel - [PATCH] sched: deliver sched_switch events to a current task

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Message-Id: <1342088069-1005148-1-git-send-email-avagin@openvz.org>
Date:	Thu, 12 Jul 2012 14:14:29 +0400
From:	Andrew Vagin <avagin@...nvz.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	linux-kernel@...r.kernel.org, Andrew Vagin <avagin@...nvz.org>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Thomas Gleixner <tglx@...utronix.de>,
	Steven Rostedt <rostedt@...dmis.org>,
	Arun Sharma <asharma@...com>
Subject: [PATCH] sched: deliver sched_switch events to a current task

Otherwise they can't be filtered for a defined task.

perf record -e sched:sched_switch ./foo

This command doesn't report any event without this patch.

I think it isn't a big problem for security, if someone will know
who will be executed next. By default perf is disabled for non-root
users.

I need this events for profiling sleep times.  sched_switch is used for
getting callchains and sched_stat_* is used for getting time periods.
This events are combined in user space, then it can be analized by
perf tools.

Cc: Ingo Molnar <mingo@...nel.org>
Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Arun Sharma <asharma@...com>
Signed-off-by: Andrew Vagin <avagin@...nvz.org>
---
 kernel/sched/core.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index d5594a4..c5d6a0f 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1910,12 +1910,12 @@ static inline void
 prepare_task_switch(struct rq *rq, struct task_struct *prev,
 		    struct task_struct *next)
 {
+	trace_sched_switch(prev, next);
 	sched_info_switch(prev, next);
 	perf_event_task_sched_out(prev, next);
 	fire_sched_out_preempt_notifiers(prev, next);
 	prepare_lock_switch(rq, next);
 	prepare_arch_switch(next);
-	trace_sched_switch(prev, next);
 }
 
 /**
-- 
1.7.1

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