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>

*** 1625,1635 ****
          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);
--- 1625,1634 ----
*** 1637,1653 ****
          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. */
--- 1636,1650 ----
*** 1701,1711 ****
                   */
                  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,
                      zio_flags, zb));
          }
  
          /* do not relocate this block */
          return (0);
--- 1698,1708 ----
                   */
                  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_SCRUB,
                      zio_flags, zb));
          }
  
          /* do not relocate this block */
          return (0);