linux-kernel - [PATCH] cfq-iosched: Add additional blktrace log messages in CFQ for easier debugging.

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Message-ID: <20100325001856.18289.83328.stgit@austin.mtv.corp.google.com>
Date:	Wed, 24 Mar 2010 17:19:34 -0700
From:	Divyesh Shah <dpshah@...gle.com>
To:	jens.axboe@...cle.com
Cc:	linux-kernel@...r.kernel.org, nauman@...gle.com, vgoyal@...hat.com,
	ctalbott@...gle.com
Subject: [PATCH] cfq-iosched: Add additional blktrace log messages in CFQ for
	easier debugging.

These extra logging messages have helped us debug some issues we've noticed in
earlier IO controller versions and should be useful now as well. The extra
logging covers:
- idling behavior. Since there are so many conditions based on which we decide
to idle or not, this patch adds a log message for some conditions that we've
found useful.
- workload slices and current prio and workload type

Signed-off-by: Divyesh Shah<dpshah@...gle.com>
---

 block/cfq-iosched.c |   17 +++++++++++++++--
 1 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index e6910dc..556124a 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -1646,6 +1646,10 @@ static struct cfq_queue *cfq_set_active_queue(struct cfq_data *cfqd,
 	if (!cfqq)
 		cfqq = cfq_get_next_queue(cfqd);
 
+	if (cfqq)
+		cfq_log_cfqq(cfqd, cfqq, "New timeslice for wl_prio:%d "
+				"wl_type:%d", cfqd->serving_prio,
+				cfqd->serving_type);
 	__cfq_set_active_queue(cfqd, cfqq);
 	return cfqq;
 }
@@ -1789,7 +1793,11 @@ static bool cfq_should_idle(struct cfq_data *cfqd, struct cfq_queue *cfqq)
 	 * Otherwise, we do only if they are the last ones
 	 * in their service tree.
 	 */
-	return service_tree->count == 1 && cfq_cfqq_sync(cfqq);
+	if (service_tree->count == 1 && cfq_cfqq_sync(cfqq))
+		return 1;
+	cfq_log_cfqq(cfqd, cfqq, "Not idling. queue_count:%d",
+			service_tree->count);
+	return 0;
 }
 
 static void cfq_arm_slice_timer(struct cfq_data *cfqd)
@@ -1834,8 +1842,11 @@ static void cfq_arm_slice_timer(struct cfq_data *cfqd)
 	 * time slice.
 	 */
 	if (sample_valid(cic->ttime_samples) &&
-	    (cfqq->slice_end - jiffies < cic->ttime_mean))
+	    (cfqq->slice_end - jiffies < cic->ttime_mean)) {
+		cfq_log_cfqq(cfqd, cfqq, "Not idling. think_time:%d",
+				cic->ttime_mean);
 		return;
+	}
 
 	cfq_mark_cfqq_wait_request(cfqq);
 
@@ -2043,6 +2054,7 @@ static void choose_service_tree(struct cfq_data *cfqd, struct cfq_group *cfqg)
 		slice = max(slice, 2 * cfqd->cfq_slice_idle);
 
 	slice = max_t(unsigned, slice, CFQ_MIN_TT);
+	cfq_log(cfqd, "workload slice:%d", slice);
 	cfqd->workload_expires = jiffies + slice;
 	cfqd->noidle_tree_requires_idle = false;
 }
@@ -3309,6 +3321,7 @@ static void cfq_completed_request(struct request_queue *q, struct request *rq)
 		if (cfq_should_wait_busy(cfqd, cfqq)) {
 			cfqq->slice_end = jiffies + cfqd->cfq_slice_idle;
 			cfq_mark_cfqq_wait_busy(cfqq);
+			cfq_log_cfqq(cfqd, cfqq, "will busy wait");
 		}
 
 		/*

--
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