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>

@@ -1625,11 +1625,10 @@
         size_t size = BP_GET_PSIZE(bp);
         spa_t *spa = dp->dp_spa;
         uint64_t phys_birth = BP_PHYSICAL_BIRTH(bp);
         boolean_t needs_io;
         int zio_flags = ZIO_FLAG_SCAN_THREAD | ZIO_FLAG_RAW | ZIO_FLAG_CANFAIL;
-        int zio_priority;
         int scan_delay = 0;
 
         if (phys_birth <= scn->scn_phys.scn_min_txg ||
             phys_birth >= scn->scn_phys.scn_max_txg)
                 return (0);

@@ -1637,17 +1636,15 @@
         count_block(dp->dp_blkstats, bp);
 
         ASSERT(DSL_SCAN_IS_SCRUB_RESILVER(scn));
         if (scn->scn_phys.scn_func == POOL_SCAN_SCRUB) {
                 zio_flags |= ZIO_FLAG_SCRUB;
-                zio_priority = ZIO_PRIORITY_SCRUB;
                 needs_io = B_TRUE;
                 scan_delay = zfs_scrub_delay;
         } else {
                 ASSERT3U(scn->scn_phys.scn_func, ==, POOL_SCAN_RESILVER);
                 zio_flags |= ZIO_FLAG_RESILVER;
-                zio_priority = ZIO_PRIORITY_RESILVER;
                 needs_io = B_FALSE;
                 scan_delay = zfs_resilver_delay;
         }
 
         /* If it's an intent log block, failure is expected. */

@@ -1701,11 +1698,11 @@
                  */
                 if (ddi_get_lbolt64() - spa->spa_last_io <= zfs_scan_idle)
                         delay(scan_delay);
 
                 zio_nowait(zio_read(NULL, spa, bp, data, size,
-                    dsl_scan_scrub_done, NULL, zio_priority,
+                    dsl_scan_scrub_done, NULL, ZIO_PRIORITY_SCRUB,
                     zio_flags, zb));
         }
 
         /* do not relocate this block */
         return (0);