writeback: trace event writeback_queue_io

Note that it adds a little overheads to account the moved/enqueued
inodes from b_dirty to b_io. The "moved" accounting may be later used to
limit the number of inodes that can be moved in one shot, in order to
keep spinlock hold time under control.

Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>

1 files changed, 25 insertions, 0 deletions

diff --git a/include/trace/events/writeback.h b/include/trace/events/writeback.h
index 898277bc89b4..205d14919ef2 100644
--- a/include/trace/events/writeback.h
+++ b/include/trace/events/writeback.h
@@ -162,6 +162,31 @@ DEFINE_WBC_EVENT(wbc_balance_dirty_written);
 DEFINE_WBC_EVENT(wbc_balance_dirty_wait);
 DEFINE_WBC_EVENT(wbc_writepage);
 
+TRACE_EVENT(writeback_queue_io,
+        TP_PROTO(struct bdi_writeback *wb,
+                 unsigned long *older_than_this,
+                 int moved),
+        TP_ARGS(wb, older_than_this, moved),
+        TP_STRUCT__entry(
+                __array(char,           name, 32)
+                __field(unsigned long,  older)
+                __field(long,           age)
+                __field(int,            moved)
+        ),
+        TP_fast_assign(
+                strncpy(__entry->name, dev_name(wb->bdi->dev), 32);
+                __entry->older  = older_than_this ?  *older_than_this : 0;
+                __entry->age    = older_than_this ?
+                                  (jiffies - *older_than_this) * 1000 / HZ : -1;
+                __entry->moved  = moved;
+        ),
+        TP_printk("bdi %s: older=%lu age=%ld enqueue=%d",
+                __entry->name,
+                __entry->older, /* older_than_this in jiffies */
+                __entry->age,   /* older_than_this in relative milliseconds */
+                __entry->moved)
+);
+
 DECLARE_EVENT_CLASS(writeback_congest_waited_template,
 
         TP_PROTO(unsigned int usec_timeout, unsigned int usec_delayed),