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>

*** 248,276 ****
   * otherwise-fatal errors, typically caused by on-disk corruption.  When
   * set, calls to zfs_panic_recover() will turn into warning messages.
   */
  int zfs_recover = 0;
  
! extern int zfs_txg_synctime_ms;
  
  /*
!  * Expiration time in units of zfs_txg_synctime_ms. This value has two
!  * meanings. First it is used to determine when the spa_deadman logic
!  * should fire. By default the spa_deadman will fire if spa_sync has
!  * not completed in 1000 * zfs_txg_synctime_ms (i.e. 1000 seconds).
!  * Secondly, the value determines if an I/O is considered "hung".
!  * Any I/O that has not completed in zfs_deadman_synctime is considered
!  * "hung" resulting in a system panic.
   */
! uint64_t zfs_deadman_synctime = 1000ULL;
  
  /*
   * Override the zfs deadman behavior via /etc/system. By default the
   * deadman is enabled except on VMware and sparc deployments.
   */
  int zfs_deadman_enabled = -1;
  
  
  /*
   * ==========================================================================
   * SPA config locking
   * ==========================================================================
--- 248,289 ----
   * otherwise-fatal errors, typically caused by on-disk corruption.  When
   * set, calls to zfs_panic_recover() will turn into warning messages.
   */
  int zfs_recover = 0;
  
! /*
!  * Expiration time in milliseconds. This value has two meanings. First it is
!  * used to determine when the spa_deadman() logic should fire. By default the
!  * spa_deadman() will fire if spa_sync() has not completed in 1000 seconds.
!  * Secondly, the value determines if an I/O is considered "hung". Any I/O that
!  * has not completed in zfs_deadman_synctime_ms is considered "hung" resulting
!  * in a system panic.
!  */
! uint64_t zfs_deadman_synctime_ms = 1000000ULL;
  
  /*
!  * Check time in milliseconds. This defines the frequency at which we check
!  * for hung I/O.
   */
! uint64_t zfs_deadman_checktime_ms = 5000ULL;
  
  /*
   * Override the zfs deadman behavior via /etc/system. By default the
   * deadman is enabled except on VMware and sparc deployments.
   */
  int zfs_deadman_enabled = -1;
  
+ /*
+  * The worst case is single-sector max-parity RAID-Z blocks, in which
+  * case the space requirement is exactly (VDEV_RAIDZ_MAXPARITY + 1)
+  * times the size; so just assume that.  Add to this the fact that
+  * we can have up to 3 DVAs per bp, and one more factor of 2 because
+  * the block may be dittoed with up to 3 DVAs by ddt_sync().  All together,
+  * the worst case is:
+  *     (VDEV_RAIDZ_MAXPARITY + 1) * SPA_DVAS_PER_BP * 2 == 24
+  */
+ int spa_asize_inflation = 24;
  
  /*
   * ==========================================================================
   * SPA config locking
   * ==========================================================================
*** 497,516 ****
  
          hdlr.cyh_func = spa_deadman;
          hdlr.cyh_arg = spa;
          hdlr.cyh_level = CY_LOW_LEVEL;
  
!         spa->spa_deadman_synctime = MSEC2NSEC(zfs_deadman_synctime *
!             zfs_txg_synctime_ms);
  
          /*
           * This determines how often we need to check for hung I/Os after
           * the cyclic has already fired. Since checking for hung I/Os is
           * an expensive operation we don't want to check too frequently.
!          * Instead wait for 5 synctimes before checking again.
           */
!         when.cyt_interval = MSEC2NSEC(5 * zfs_txg_synctime_ms);
          when.cyt_when = CY_INFINITY;
          mutex_enter(&cpu_lock);
          spa->spa_deadman_cycid = cyclic_add(&hdlr, &when);
          mutex_exit(&cpu_lock);
  
--- 510,528 ----
  
          hdlr.cyh_func = spa_deadman;
          hdlr.cyh_arg = spa;
          hdlr.cyh_level = CY_LOW_LEVEL;
  
!         spa->spa_deadman_synctime = MSEC2NSEC(zfs_deadman_synctime_ms);
  
          /*
           * This determines how often we need to check for hung I/Os after
           * the cyclic has already fired. Since checking for hung I/Os is
           * an expensive operation we don't want to check too frequently.
!          * Instead wait for 5 seconds before checking again.
           */
!         when.cyt_interval = MSEC2NSEC(zfs_deadman_checktime_ms);
          when.cyt_when = CY_INFINITY;
          mutex_enter(&cpu_lock);
          spa->spa_deadman_cycid = cyclic_add(&hdlr, &when);
          mutex_exit(&cpu_lock);
  
*** 1497,1514 ****
  
  /* ARGSUSED */
  uint64_t
  spa_get_asize(spa_t *spa, uint64_t lsize)
  {
!         /*
!          * The worst case is single-sector max-parity RAID-Z blocks, in which
!          * case the space requirement is exactly (VDEV_RAIDZ_MAXPARITY + 1)
!          * times the size; so just assume that.  Add to this the fact that
!          * we can have up to 3 DVAs per bp, and one more factor of 2 because
!          * the block may be dittoed with up to 3 DVAs by ddt_sync().
!          */
!         return (lsize * (VDEV_RAIDZ_MAXPARITY + 1) * SPA_DVAS_PER_BP * 2);
  }
  
  uint64_t
  spa_get_dspace(spa_t *spa)
  {
--- 1509,1519 ----
  
  /* ARGSUSED */
  uint64_t
  spa_get_asize(spa_t *spa, uint64_t lsize)
  {
!         return (lsize * spa_asize_inflation);
  }
  
  uint64_t
  spa_get_dspace(spa_t *spa)
  {