4045 zfs write throttle & i/o scheduler performance work
Reviewed by: George Wilson <george.wilson@delphix.com>
Reviewed by: Adam Leventhal <ahl@delphix.com>
Reviewed by: Christopher Siden <christopher.siden@delphix.com>

*** 16,25 ****
--- 16,26 ----
   * fields enclosed by brackets "[]" replaced with your own identifying
   * information: Portions Copyright [yyyy] [name of copyright owner]
   *
   * CDDL HEADER END
   */
+ 
  /*
   * Copyright 2009 Sun Microsystems, Inc.  All rights reserved.
   * Use is subject to license terms.
   */
  
*** 87,101 ****
--- 88,105 ----
   * every cpu (see txg_quiesce()).
   */
  typedef struct tx_state {
          tx_cpu_t        *tx_cpu;        /* protects access to tx_open_txg */
          kmutex_t        tx_sync_lock;   /* protects the rest of this struct */
+ 
          uint64_t        tx_open_txg;    /* currently open txg id */
          uint64_t        tx_quiesced_txg; /* quiesced txg waiting for sync */
          uint64_t        tx_syncing_txg; /* currently syncing txg id */
          uint64_t        tx_synced_txg;  /* last synced txg id */
  
+         hrtime_t        tx_open_time;   /* start time of tx_open_txg */
+ 
          uint64_t        tx_sync_txg_waiting; /* txg we're waiting to sync */
          uint64_t        tx_quiesce_txg_waiting; /* txg we're waiting to open */
  
          kcondvar_t      tx_sync_more_cv;
          kcondvar_t      tx_sync_done_cv;