writeback: add new tracepoints

Add 2 new trace points to the periodic write-back wake up case, just like we do
in the 'bdi_queue_work()' function. Namely, introduce:

1. trace_writeback_wake_thread(bdi)
2. trace_writeback_wake_forker_thread(bdi)

The first event is triggered every time we wake up a bdi thread to start
periodic background write-out. The second event is triggered only when the bdi
thread does not exist and should be created by the forker thread.

This patch was suggested by Dave Chinner and Christoph Hellwig.

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>

diff --git a/include/trace/events/writeback.h b/include/trace/events/writeback.h
index 84ab72df953cb5492063c35d5da56d8ad9a3487c..f345f66ae9d100d755c4e4a1afb3f4b2310148da 100644 (file)
--- a/include/trace/events/writeback.h
+++ b/include/trace/events/writeback.h
@@ -81,6 +81,8 @@ DEFINE_EVENT(writeback_class, name, \
        TP_ARGS(bdi))
 
 DEFINE_WRITEBACK_EVENT(writeback_nowork);
+DEFINE_WRITEBACK_EVENT(writeback_wake_thread);
+DEFINE_WRITEBACK_EVENT(writeback_wake_forker_thread);
 DEFINE_WRITEBACK_EVENT(writeback_bdi_register);
 DEFINE_WRITEBACK_EVENT(writeback_bdi_unregister);
 DEFINE_WRITEBACK_EVENT(writeback_thread_start);

diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index 99890831d55714a14e32ec6ab8876b93a0a2fa74..9008c4e207f66ca047d99bd86cb530157f7723a2 100644 (file)
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -310,6 +310,7 @@ static void wakeup_timer_fn(unsigned long data)
 
        spin_lock_bh(&bdi->wb_lock);
        if (bdi->wb.task) {
+               trace_writeback_wake_thread(bdi);
                wake_up_process(bdi->wb.task);
        } else {
                /*
@@ -317,6 +318,7 @@ static void wakeup_timer_fn(unsigned long data)
                 * In this case we have to wake-up the forker thread which
                 * should create and run the bdi thread.
                 */
+               trace_writeback_wake_forker_thread(bdi);
                wake_up_process(default_backing_dev_info.wb.task);
        }
        spin_unlock_bh(&bdi->wb_lock);