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Commit 52bb9198 authored by Mel Gorman's avatar Mel Gorman Committed by Linus Torvalds
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writeback: account for time spent congestion_waited 



There is strong evidence to indicate a lot of time is being spent in
congestion_wait(), some of it unnecessarily.  This patch adds a tracepoint
for congestion_wait to record when congestion_wait() was called, how long
the timeout was for and how long it actually slept.

Signed-off-by: default avatarMel Gorman <mel@csn.ul.ie>
Reviewed-by: default avatarMinchan Kim <minchan.kim@gmail.com>
Reviewed-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Rik van Riel <riel@redhat.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent e11da5b4

include/trace/events/writeback.h

+28 −0
Original line number Diff line number Diff line
@@ -151,6 +151,34 @@ DEFINE_WBC_EVENT(wbc_balance_dirty_written); 
DEFINE_WBC_EVENT(wbc_balance_dirty_wait);

DEFINE_WBC_EVENT(wbc_writepage);



DECLARE_EVENT_CLASS(writeback_congest_waited_template,



	TP_PROTO(unsigned int usec_timeout, unsigned int usec_delayed),



	TP_ARGS(usec_timeout, usec_delayed),



	TP_STRUCT__entry(

		__field(	unsigned int,	usec_timeout	)

		__field(	unsigned int,	usec_delayed	)

	),



	TP_fast_assign(

		__entry->usec_timeout	= usec_timeout;

		__entry->usec_delayed	= usec_delayed;

	),



	TP_printk("usec_timeout=%u usec_delayed=%u",

			__entry->usec_timeout,

			__entry->usec_delayed)

);



DEFINE_EVENT(writeback_congest_waited_template, writeback_congestion_wait,



	TP_PROTO(unsigned int usec_timeout, unsigned int usec_delayed),



	TP_ARGS(usec_timeout, usec_delayed)

);



#endif /* _TRACE_WRITEBACK_H */



/* This part must be outside protection */

mm/backing-dev.c

+5 −0
Original line number Diff line number Diff line
@@ -764,12 +764,17 @@ EXPORT_SYMBOL(set_bdi_congested); 
long congestion_wait(int sync, long timeout)

{

	long ret;

	unsigned long start = jiffies;

	DEFINE_WAIT(wait);

	wait_queue_head_t *wqh = &congestion_wqh[sync];



	prepare_to_wait(wqh, &wait, TASK_UNINTERRUPTIBLE);

	ret = io_schedule_timeout(timeout);

	finish_wait(wqh, &wait);



	trace_writeback_congestion_wait(jiffies_to_usecs(timeout),

					jiffies_to_usecs(jiffies - start));



	return ret;

}

EXPORT_SYMBOL(congestion_wait);