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>

@@ -248,29 +248,42 @@
  * 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 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;
 
 /*
- * 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.
+ * Check time in milliseconds. This defines the frequency at which we check
+ * for hung I/O.
  */
-uint64_t zfs_deadman_synctime = 1000ULL;
+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
  * ==========================================================================

@@ -497,20 +510,19 @@
 
         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);
+        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 synctimes before checking again.
+         * Instead wait for 5 seconds before checking again.
          */
-        when.cyt_interval = MSEC2NSEC(5 * zfs_txg_synctime_ms);
+        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);
 

@@ -1497,18 +1509,11 @@
 
 /* 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);
+        return (lsize * spa_asize_inflation);
 }
 
 uint64_t
 spa_get_dspace(spa_t *spa)
 {