jbd2: track request delay statistics

Track the delay between when we first request that the commit begin
and when it actually begins, so we can see how much of a gap exists.
In theory, this should just be the remaining scheduling quantuum of
the thread which requested the commit (assuming it was not a
synchronous operation which triggered the commit request) plus
scheduling overhead; however, it's possible that real time processes
might get in the way of letting the kjournald thread from executing.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

1 files changed, 7 insertions, 0 deletions

diff --git a/include/linux/jbd2.h b/include/linux/jbd2.h
index e30b663..e0aafc4 100644
--- a/include/linux/jbd2.h
+++ b/include/linux/jbd2.h
@@ -581,6 +581,11 @@ struct transaction_s
 	unsigned long		t_start;
 
 	/*
+	 * When commit was requested
+	 */
+	unsigned long		t_requested;
+
+	/*
 	 * Checkpointing stats [j_checkpoint_sem]
 	 */
 	struct transaction_chp_stats_s t_chp_stats;
@@ -637,6 +642,7 @@ struct transaction_s
 
 struct transaction_run_stats_s {
 	unsigned long		rs_wait;
+	unsigned long		rs_request_delay;
 	unsigned long		rs_running;
 	unsigned long		rs_locked;
 	unsigned long		rs_flushing;
@@ -649,6 +655,7 @@ struct transaction_run_stats_s {
 
 struct transaction_stats_s {
 	unsigned long		ts_tid;
+	unsigned long		ts_requested;
 	struct transaction_run_stats_s run;
 };