[patch 05/15] LTTng instrumentation - scheduler

From: Mathieu Desnoyers
Date: Wed Jul 09 2008 - 11:02:20 EST

Instrument the scheduler activity (sched_switch, migration, wakeups, wait for a
task, signal delivery) and process/thread creation/destruction (fork, exit,
kthread stop). Actually, kthread creation is not instrumented in this patch
because it is architecture dependent. It allows to connect tracers such as
ftrace which detects scheduling latencies, good/bad scheduler decisions. Tools
like LTTng can export this scheduler information along with instrumentation of
the rest of the kernel activity to perform post-mortem analysis on the scheduler
activity.

About the performance impact of tracepoints (which is comparable to markers),
even without immediate values optimizations, tests done by Hideo Aoki on ia64
show no regression. His test case was using hackbench on a kernel where
scheduler instrumentation (about 5 events in code scheduler code) was added.
See the "Tracepoints" patch header for performance result detail.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxx>
CC: 'Peter Zijlstra' <peterz@xxxxxxxxxxxxx>
CC: 'Steven Rostedt' <rostedt@xxxxxxxxxxx>
CC: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CC: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
CC: "Frank Ch. Eigler" <fche@xxxxxxxxxx>
CC: 'Ingo Molnar' <mingo@xxxxxxx>
CC: 'Hideo AOKI' <haoki@xxxxxxxxxx>
CC: Takashi Nishiie <t-nishiie@xxxxxxxxxxxxxxxxxx>
CC: Eduard - Gabriel Munteanu <eduard.munteanu@xxxxxxxxxxx>
---
kernel/exit.c | 6 ++++++
kernel/fork.c | 3 +++
kernel/kthread.c | 5 +++++
kernel/sched-trace.h | 43 +++++++++++++++++++++++++++++++++++++++++++
kernel/sched.c | 4 ++++
kernel/signal.c | 3 +++
6 files changed, 64 insertions(+)

Index: linux-2.6-lttng/kernel/kthread.c
===================================================================
--- linux-2.6-lttng.orig/kernel/kthread.c 2008-07-09 10:55:46.000000000 -0400
+++ linux-2.6-lttng/kernel/kthread.c 2008-07-09 10:57:43.000000000 -0400
@@ -13,6 +13,7 @@
#include <linux/file.h>
#include <linux/module.h>
#include <linux/mutex.h>
+#include "sched-trace.h"

#define KTHREAD_NICE_LEVEL (-5)

@@ -187,6 +188,8 @@ int kthread_stop(struct task_struct *k)
/* It could exit after stop_info.k set, but before wake_up_process. */
get_task_struct(k);

+ trace_sched_kthread_stop(k);
+
/* Must init completion *before* thread sees kthread_stop_info.k */
init_completion(&kthread_stop_info.done);
smp_wmb();
@@ -202,6 +205,8 @@ int kthread_stop(struct task_struct *k)
ret = kthread_stop_info.err;
mutex_unlock(&kthread_stop_lock);

+ trace_sched_kthread_stop_ret(ret);
+
return ret;
}
EXPORT_SYMBOL(kthread_stop);
Index: linux-2.6-lttng/kernel/sched.c
===================================================================
--- linux-2.6-lttng.orig/kernel/sched.c 2008-07-09 10:55:46.000000000 -0400
+++ linux-2.6-lttng/kernel/sched.c 2008-07-09 10:57:43.000000000 -0400
@@ -1987,6 +1987,7 @@ void wait_task_inactive(struct task_stru
* just go back and repeat.
*/
rq = task_rq_lock(p, &flags);
+ trace_sched_wait_task(p);
running = task_running(rq, p);
on_rq = p->se.on_rq;
task_rq_unlock(rq, &flags);
@@ -2275,6 +2276,7 @@ static int try_to_wake_up(struct task_st

smp_wmb();
rq = task_rq_lock(p, &flags);
+ trace_sched_try_wakeup(p);
old_state = p->state;
if (!(old_state & state))
goto out;
@@ -2457,6 +2459,7 @@ void wake_up_new_task(struct task_struct
struct rq *rq;

rq = task_rq_lock(p, &flags);
+ trace_sched_wakeup_new_task(p);
BUG_ON(p->state != TASK_RUNNING);
update_rq_clock(rq);

@@ -2884,6 +2887,7 @@ static void sched_migrate_task(struct ta
|| unlikely(cpu_is_offline(dest_cpu)))
goto out;

+ trace_sched_migrate_task(p, dest_cpu);
/* force the process onto the specified CPU */
if (migrate_task(p, dest_cpu, &req)) {
/* Need to wait for migration thread (might exit: take ref). */
Index: linux-2.6-lttng/kernel/exit.c
===================================================================
--- linux-2.6-lttng.orig/kernel/exit.c 2008-07-09 10:55:46.000000000 -0400
+++ linux-2.6-lttng/kernel/exit.c 2008-07-09 10:57:43.000000000 -0400
@@ -46,6 +46,7 @@
#include <linux/resource.h>
#include <linux/blkdev.h>
#include <linux/task_io_accounting_ops.h>
+#include "sched-trace.h"

#include <asm/uaccess.h>
#include <asm/unistd.h>
@@ -149,6 +150,7 @@ static void __exit_signal(struct task_st

static void delayed_put_task_struct(struct rcu_head *rhp)
{
+ trace_sched_process_free(container_of(rhp, struct task_struct, rcu));
put_task_struct(container_of(rhp, struct task_struct, rcu));
}

@@ -1040,6 +1042,8 @@ NORET_TYPE void do_exit(long code)

if (group_dead)
acct_process();
+ trace_sched_process_exit(tsk);
+
exit_sem(tsk);
exit_files(tsk);
exit_fs(tsk);
@@ -1524,6 +1528,8 @@ static long do_wait(enum pid_type type,
struct task_struct *tsk;
int flag, retval;

+ trace_sched_process_wait(pid);
+
add_wait_queue(&current->signal->wait_chldexit,&wait);
repeat:
/* If there is nothing that can match our critier just get out */
Index: linux-2.6-lttng/kernel/fork.c
===================================================================
--- linux-2.6-lttng.orig/kernel/fork.c 2008-07-09 10:55:46.000000000 -0400
+++ linux-2.6-lttng/kernel/fork.c 2008-07-09 10:58:05.000000000 -0400
@@ -56,6 +56,7 @@
#include <linux/proc_fs.h>
#include <linux/blkdev.h>
#include <linux/magic.h>
+#include "sched-trace.h"

#include <asm/pgtable.h>
#include <asm/pgalloc.h>
@@ -1362,6 +1363,8 @@ long do_fork(unsigned long clone_flags,
if (!IS_ERR(p)) {
struct completion vfork;

+ trace_sched_process_fork(current, p);
+
nr = task_pid_vnr(p);

if (clone_flags & CLONE_PARENT_SETTID)
Index: linux-2.6-lttng/kernel/signal.c
===================================================================
--- linux-2.6-lttng.orig/kernel/signal.c 2008-07-09 10:46:33.000000000 -0400
+++ linux-2.6-lttng/kernel/signal.c 2008-07-09 10:57:43.000000000 -0400
@@ -26,6 +26,7 @@
#include <linux/freezer.h>
#include <linux/pid_namespace.h>
#include <linux/nsproxy.h>
+#include "sched-trace.h"

#include <asm/param.h>
#include <asm/uaccess.h>
@@ -807,6 +808,8 @@ static int send_signal(int sig, struct s
struct sigpending *pending;
struct sigqueue *q;

+ trace_sched_signal_send(sig, t);
+
assert_spin_locked(&t->sighand->siglock);
if (!prepare_signal(sig, t))
return 0;
Index: linux-2.6-lttng/kernel/sched-trace.h
===================================================================
--- /dev/null 1970-01-01 00:00:00.000000000 +0000
+++ linux-2.6-lttng/kernel/sched-trace.h 2008-07-09 10:57:43.000000000 -0400
@@ -0,0 +1,43 @@
+#ifndef _SCHED_TRACE_H
+#define _SCHED_TRACE_H
+
+#include <linux/tracepoint.h>
+
+DEFINE_TRACE(sched_kthread_stop,
+ TPPROTO(struct task_struct *t),
+ TPARGS(t));
+DEFINE_TRACE(sched_kthread_stop_ret,
+ TPPROTO(int ret),
+ TPARGS(ret));
+DEFINE_TRACE(sched_wait_task,
+ TPPROTO(struct task_struct *p),
+ TPARGS(p));
+DEFINE_TRACE(sched_try_wakeup,
+ TPPROTO(struct task_struct *p),
+ TPARGS(p));
+DEFINE_TRACE(sched_wakeup_new_task,
+ TPPROTO(struct task_struct *p),
+ TPARGS(p));
+DEFINE_TRACE(sched_switch,
+ TPPROTO(struct task_struct *prev, struct task_struct *next),
+ TPARGS(prev, next));
+DEFINE_TRACE(sched_migrate_task,
+ TPPROTO(struct task_struct *p, int dest_cpu),
+ TPARGS(p, dest_cpu));
+DEFINE_TRACE(sched_process_free,
+ TPPROTO(struct task_struct *p),
+ TPARGS(p));
+DEFINE_TRACE(sched_process_exit,
+ TPPROTO(struct task_struct *p),
+ TPARGS(p));
+DEFINE_TRACE(sched_process_wait,
+ TPPROTO(struct pid *pid),
+ TPARGS(pid));
+DEFINE_TRACE(sched_process_fork,
+ TPPROTO(struct task_struct *parent, struct task_struct *child),
+ TPARGS(parent, child));
+DEFINE_TRACE(sched_signal_send,
+ TPPROTO(int sig, struct task_struct *p),
+ TPARGS(sig, p));
+
+#endif

--
Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/