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Subject: [PATCH v3 3/3] block/diskstats: replace time_in_queue with sum of
 request times
From:   Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
To:     linux-block@vger.kernel.org, Jens Axboe <axboe@kernel.dk>,
        linux-kernel@vger.kernel.org
Cc:     Mikulas Patocka <mpatocka@redhat.com>,
        Mike Snitzer <snitzer@redhat.com>,
        Ming Lei <ming.lei@redhat.com>
Date:   Tue, 24 Mar 2020 09:39:46 +0300
Message-ID: <158503198613.1955.12660218488410753545.stgit@buzz>
In-Reply-To: <158503038812.1955.7827988255138056389.stgit@buzz>
References: <158503038812.1955.7827988255138056389.stgit@buzz>
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Column "time_in_queue" in diskstats is supposed to show total waiting time
of all requests. I.e. value should be equal to the sum of times from other
columns. But this is not true, because column "time_in_queue" is counted
separately in jiffies rather than in nanoseconds as other times.

This patch removes redundant counter for "time_in_queue" and shows total
time of read, write, discard and flush requests.

Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
---
 block/bio.c               |    1 -
 block/blk-core.c          |    1 -
 block/genhd.c             |    7 +++++--
 block/partition-generic.c |    6 +++++-
 include/linux/genhd.h     |    1 -
 5 files changed, 10 insertions(+), 6 deletions(-)

diff --git a/block/bio.c b/block/bio.c
index b1053eb7af37..a353d5cdf589 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -1805,7 +1805,6 @@ void generic_end_io_acct(struct request_queue *q, int req_op,
 
 	update_io_ticks(part, now, true);
 	part_stat_add(part, nsecs[sgrp], jiffies_to_nsecs(duration));
-	part_stat_add(part, time_in_queue, duration);
 	part_dec_in_flight(q, part, op_is_write(req_op));
 
 	part_stat_unlock();
diff --git a/block/blk-core.c b/block/blk-core.c
index 4401b30a1751..eaf6cb3887e6 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1340,7 +1340,6 @@ void blk_account_io_done(struct request *req, u64 now)
 		update_io_ticks(part, jiffies, true);
 		part_stat_inc(part, ios[sgrp]);
 		part_stat_add(part, nsecs[sgrp], now - req->start_time_ns);
-		part_stat_add(part, time_in_queue, nsecs_to_jiffies64(now - req->start_time_ns));
 		part_dec_in_flight(req->q, part, rq_data_dir(req));
 
 		hd_struct_put(part);
diff --git a/block/genhd.c b/block/genhd.c
index 606e8755f6ed..2b49d997ac72 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -87,7 +87,6 @@ void part_stat_read_all(struct hd_struct *part, struct disk_stats *stat)
 		}
 
 		stat->io_ticks += ptr->io_ticks;
-		stat->time_in_queue += ptr->time_in_queue;
 	}
 }
 #endif /* CONFIG_SMP */
@@ -1487,7 +1486,11 @@ static int diskstats_show(struct seq_file *seqf, void *v)
 							NSEC_PER_MSEC),
 			   inflight,
 			   jiffies_to_msecs(stat.io_ticks),
-			   jiffies_to_msecs(stat.time_in_queue),
+			   (unsigned int)div_u64(stat.nsecs[STAT_READ] +
+						 stat.nsecs[STAT_WRITE] +
+						 stat.nsecs[STAT_DISCARD] +
+						 stat.nsecs[STAT_FLUSH],
+							NSEC_PER_MSEC),
 			   stat.ios[STAT_DISCARD],
 			   stat.merges[STAT_DISCARD],
 			   stat.sectors[STAT_DISCARD],
diff --git a/block/partition-generic.c b/block/partition-generic.c
index 6d3fcb5187cb..2a9bc78a116f 100644
--- a/block/partition-generic.c
+++ b/block/partition-generic.c
@@ -143,7 +143,11 @@ ssize_t part_stat_show(struct device *dev,
 		(unsigned int)div_u64(stat.nsecs[STAT_WRITE], NSEC_PER_MSEC),
 		inflight,
 		jiffies_to_msecs(stat.io_ticks),
-		jiffies_to_msecs(stat.time_in_queue),
+		(unsigned int)div_u64(stat.nsecs[STAT_READ] +
+				      stat.nsecs[STAT_WRITE] +
+				      stat.nsecs[STAT_DISCARD] +
+				      stat.nsecs[STAT_FLUSH],
+						NSEC_PER_MSEC),
 		stat.ios[STAT_DISCARD],
 		stat.merges[STAT_DISCARD],
 		(unsigned long long)stat.sectors[STAT_DISCARD],
diff --git a/include/linux/genhd.h b/include/linux/genhd.h
index ead3ffb7f327..019ede22ebd2 100644
--- a/include/linux/genhd.h
+++ b/include/linux/genhd.h
@@ -89,7 +89,6 @@ struct disk_stats {
 	unsigned long ios[NR_STAT_GROUPS];
 	unsigned long merges[NR_STAT_GROUPS];
 	unsigned long io_ticks;
-	unsigned long time_in_queue;
 	local_t in_flight[2];
 };