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>
diff --git a/include/trace/events/writeback.h b/include/trace/events/writeback.h
index 898277b..205d149 100644
--- a/include/trace/events/writeback.h
+++ b/include/trace/events/writeback.h
@@ -162,6 +162,31 @@
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),