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Subject[PATCH 3/4] dm: Compute average flush time from component devices
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For dm devices which are composed of other block devices, a flush is mapped out
to those other block devices. Therefore, the average flush time can be
computed as the average flush time of whichever device flushes most slowly.

Signed-off-by: Darrick J. Wong <djwong@us.ibm.com>
---
drivers/md/dm.c | 28 ++++++++++++++++++++++++++++
1 files changed, 28 insertions(+), 0 deletions(-)


diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 7cb1352..62aeeb9 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -846,12 +846,38 @@ static void start_queue(struct request_queue *q)
spin_unlock_irqrestore(q->queue_lock, flags);
}

+static void measure_flushes(struct mapped_device *md)
+{
+ struct dm_table *t;
+ struct dm_dev_internal *dd;
+ struct list_head *devices;
+ u64 max = 0, samples = 0;
+
+ t = dm_get_live_table(md);
+ devices = dm_table_get_devices(t);
+ list_for_each_entry(dd, devices, list) {
+ if (dd->dm_dev.bdev->bd_disk->avg_flush_time_ns <= max)
+ continue;
+ max = dd->dm_dev.bdev->bd_disk->avg_flush_time_ns;
+ samples = dd->dm_dev.bdev->bd_disk->flush_samples;
+ }
+ dm_table_put(t);
+
+ spin_lock(&md->disk->flush_time_lock);
+ md->disk->avg_flush_time_ns = max;
+ md->disk->flush_samples = samples;
+ spin_unlock(&md->disk->flush_time_lock);
+}
+
static void dm_done(struct request *clone, int error, bool mapped)
{
int r = error;
struct dm_rq_target_io *tio = clone->end_io_data;
dm_request_endio_fn rq_end_io = tio->ti->type->rq_end_io;

+ if (clone->cmd_flags & REQ_FLUSH)
+ measure_flushes(tio->md);
+
if (mapped && rq_end_io)
r = rq_end_io(tio->ti, clone, error, &tio->info);

@@ -2310,6 +2336,8 @@ static void dm_wq_work(struct work_struct *work)
if (dm_request_based(md))
generic_make_request(c);
else
+ if (c->bi_rw & REQ_FLUSH)
+ measure_flushes(md);
__split_and_process_bio(md, c);

down_read(&md->io_lock);


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