Call gethrtime() only once per new txg creation

When transitioning current open TXG into QUIESCE state and opening
a new one txg_quiesce() calls gethrtime():
  - to mark the birth time of the new TXG
  - to record the SPA txg history kstat
  - implicitely inside spa_txg_history_add()

These timestamps are practically the same, so that the first one
can be used instead of the other two.  The only visible difference
is that inside spa_txg_history_add() the time spent in kmem_zalloc()
will be counted towards the opened TXG.

Since at this point the new TXG already exists (tx->tx_open_txg
has been already incremented) it is actually a correct accounting.

In any case this extra work is only happening when spa_txg_history
kstat is activated (i.e. zfs_txg_history > 0) and doesn't affect
the normal processing in any way.

Signed-off-by: Cyril Plisko <[email protected]>
Issue #2075

1 files changed, 2 insertions, 2 deletions

diff --git a/module/zfs/spa_stats.c b/module/zfs/spa_stats.c
index 2576d867f..a94fecfe8 100644
--- a/module/zfs/spa_stats.c
+++ b/module/zfs/spa_stats.c
@@ -422,7 +422,7 @@ spa_txg_history_destroy(spa_t *spa)
  * Add a new txg to historical record.
  */
 void
-spa_txg_history_add(spa_t *spa, uint64_t txg)
+spa_txg_history_add(spa_t *spa, uint64_t txg, hrtime_t birth_time)
 {
 	spa_stats_history_t *ssh = &spa->spa_stats.txg_history;
 	spa_txg_history_t *sth, *rm;
@@ -433,7 +433,7 @@ spa_txg_history_add(spa_t *spa, uint64_t txg)
 	sth = kmem_zalloc(sizeof (spa_txg_history_t), KM_PUSHPAGE);
 	sth->txg = txg;
 	sth->state = TXG_STATE_OPEN;
-	sth->times[TXG_STATE_BIRTH] = gethrtime();
+	sth->times[TXG_STATE_BIRTH] = birth_time;
 
 	mutex_enter(&ssh->lock);