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>

@@ -870,11 +870,11 @@
                     ZIO_FLAG_CANFAIL);
         }
         if (lwb->lwb_zio == NULL) {
                 lwb->lwb_zio = zio_rewrite(zilog->zl_root_zio, zilog->zl_spa,
                     0, &lwb->lwb_blk, lwb->lwb_buf, BP_GET_LSIZE(&lwb->lwb_blk),
-                    zil_lwb_write_done, lwb, ZIO_PRIORITY_LOG_WRITE,
+                    zil_lwb_write_done, lwb, ZIO_PRIORITY_SYNC_WRITE,
                     ZIO_FLAG_CANFAIL | ZIO_FLAG_DONT_PROPAGATE, &zb);
         }
 }
 
 /*