writeback: Initial tracing support

Trace queue/sched/exec parts of the writeback loop. This provides
insight into when and why flusher threads are scheduled to run. e.g
a sync invocation leaves traces like:

     sync-[...]: writeback_queue: bdi 8:0: sb_dev 8:1 nr_pages=7712 sync_mode=0 kupdate=0 range_cyclic=0 background=0
flush-8:0-[...]: writeback_exec: bdi 8:0: sb_dev 8:1 nr_pages=7712 sync_mode=0 kupdate=0 range_cyclic=0 background=0

This also lays the foundation for adding more writeback tracing to
provide deeper insight into the whole writeback path.

The original tracing code is from Jens Axboe, though this version is
a rewrite as a result of the code being traced changing
significantly.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>

1 files changed, 91 insertions, 0 deletions

diff --git a/include/trace/events/writeback.h b/include/trace/events/writeback.h
new file mode 100644
index 000000000000..562fcae10d9d
--- /dev/null
+++ b/include/trace/events/writeback.h
@@ -0,0 +1,91 @@
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM writeback
+
+#if !defined(_TRACE_WRITEBACK_H) || defined(TRACE_HEADER_MULTI_READ)
+#define _TRACE_WRITEBACK_H
+
+#include <linux/backing-dev.h>
+#include <linux/writeback.h>
+
+struct wb_writeback_work;
+
+DECLARE_EVENT_CLASS(writeback_work_class,
+        TP_PROTO(struct backing_dev_info *bdi, struct wb_writeback_work *work),
+        TP_ARGS(bdi, work),
+        TP_STRUCT__entry(
+                __array(char, name, 32)
+                __field(long, nr_pages)
+                __field(dev_t, sb_dev)
+                __field(int, sync_mode)
+                __field(int, for_kupdate)
+                __field(int, range_cyclic)
+                __field(int, for_background)
+        ),
+        TP_fast_assign(
+                strncpy(__entry->name, dev_name(bdi->dev), 32);
+                __entry->nr_pages = work->nr_pages;
+                __entry->sb_dev = work->sb ? work->sb->s_dev : 0;
+                __entry->sync_mode = work->sync_mode;
+                __entry->for_kupdate = work->for_kupdate;
+                __entry->range_cyclic = work->range_cyclic;
+                __entry->for_background = work->for_background;
+        ),
+        TP_printk("bdi %s: sb_dev %d:%d nr_pages=%ld sync_mode=%d "
+                  "kupdate=%d range_cyclic=%d background=%d",
+                  __entry->name,
+                  MAJOR(__entry->sb_dev), MINOR(__entry->sb_dev),
+                  __entry->nr_pages,
+                  __entry->sync_mode,
+                  __entry->for_kupdate,
+                  __entry->range_cyclic,
+                  __entry->for_background
+        )
+);
+#define DEFINE_WRITEBACK_WORK_EVENT(name) \
+DEFINE_EVENT(writeback_work_class, name, \
+        TP_PROTO(struct backing_dev_info *bdi, struct wb_writeback_work *work), \
+        TP_ARGS(bdi, work))
+DEFINE_WRITEBACK_WORK_EVENT(writeback_nothread);
+DEFINE_WRITEBACK_WORK_EVENT(writeback_queue);
+DEFINE_WRITEBACK_WORK_EVENT(writeback_exec);
+
+TRACE_EVENT(writeback_pages_written,
+        TP_PROTO(long pages_written),
+        TP_ARGS(pages_written),
+        TP_STRUCT__entry(
+                __field(long,           pages)
+        ),
+        TP_fast_assign(
+                __entry->pages          = pages_written;
+        ),
+        TP_printk("%ld", __entry->pages)
+);
+
+DECLARE_EVENT_CLASS(writeback_class,
+        TP_PROTO(struct backing_dev_info *bdi),
+        TP_ARGS(bdi),
+        TP_STRUCT__entry(
+                __array(char, name, 32)
+        ),
+        TP_fast_assign(
+                strncpy(__entry->name, dev_name(bdi->dev), 32);
+        ),
+        TP_printk("bdi %s",
+                  __entry->name
+        )
+);
+#define DEFINE_WRITEBACK_EVENT(name) \
+DEFINE_EVENT(writeback_class, name, \
+        TP_PROTO(struct backing_dev_info *bdi), \
+        TP_ARGS(bdi))
+
+DEFINE_WRITEBACK_EVENT(writeback_nowork);
+DEFINE_WRITEBACK_EVENT(writeback_bdi_register);
+DEFINE_WRITEBACK_EVENT(writeback_bdi_unregister);
+DEFINE_WRITEBACK_EVENT(writeback_thread_start);
+DEFINE_WRITEBACK_EVENT(writeback_thread_stop);
+
+#endif /* _TRACE_WRITEBACK_H */
+
+/* This part must be outside protection */
+#include <trace/define_trace.h>