tracing, sched: LTTng instrumentation - scheduler

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.

Changelog :

- Change instrumentation location and parameter to match ftrace
  instrumentation, previously done with kernel markers.

[ mingo@elte.hu: conflict resolutions ]
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Acked-by: 'Peter Zijlstra' <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 5 insertions, 0 deletions

diff --git a/kernel/kthread.c b/kernel/kthread.c
index 96cff2f8710b..50598e29439a 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -13,6 +13,7 @@
 #include <linux/file.h>
 #include <linux/module.h>
 #include <linux/mutex.h>
+#include <trace/sched.h>
 
 #define KTHREAD_NICE_LEVEL (-5)
 
@@ -206,6 +207,8 @@ 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();
@@ -221,6 +224,8 @@ 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);