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Call gethrtime() only once per new txg creation

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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 <cyril.plisko@mountall.com>
Issue #2075
This commit is contained in:
Cyril Plisko
2014-01-15 11:26:12 +02:00
committed by Brian Behlendorf
parent 478d64fdae
commit 01b738f457
3 changed files with 5 additions and 5 deletions
Download Patch File Download Diff File Expand all files Collapse all files
module/zfs/txg.c
+2 -2
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@@ -377,8 +377,8 @@ txg_quiesce(dsl_pool_t *dp, uint64_t txg)
tx->tx_open_txg++;
tx->tx_open_time = gethrtime();
spa_txg_history_set(dp->dp_spa, txg, TXG_STATE_OPEN, gethrtime());
spa_txg_history_add(dp->dp_spa, tx->tx_open_txg);
spa_txg_history_set(dp->dp_spa, txg, TXG_STATE_OPEN, tx->tx_open_time);
spa_txg_history_add(dp->dp_spa, tx->tx_open_txg, tx->tx_open_time);
DTRACE_PROBE2(txg__quiescing, dsl_pool_t *, dp, uint64_t, txg);
DTRACE_PROBE2(txg__opened, dsl_pool_t *, dp, uint64_t, tx->tx_open_txg);