OS-7753 THREAD_KPRI_RELEASE does nothing of the sort
Reviewed by: Bryan Cantrill <bryan@joyent.com>
Reviewed by: Jerry Jelinek <jerry.jelinek@joyent.com>

*** 19,28 ****
--- 19,29 ----
   * CDDL HEADER END
   */
  /*
   * Copyright 2009 Sun Microsystems, Inc.  All rights reserved.
   * Use is subject to license terms.
+  * Copyright 2019 Joyent, Inc.
   */
  
  /* Copyright (c) 1983, 1984, 1985, 1986, 1987, 1988, 1989 AT&T */
  /* All Rights Reserved */
  
*** 219,262 ****
  
  /*
   * Wait for all of the direct IO operations to finish
   */
  
- uint32_t        ufs_directio_drop_kpri = 0;     /* enable kpri hack */
- 
  static int
  directio_wait(struct directio_buf *tail, long *bytes_iop)
  {
          int     error = 0, newerror;
          struct directio_buf     *dbp;
-         uint_t  kpri_req_save;
  
          /*
           * The linked list of directio buf structures is maintained
           * in reverse order (tail->last request->penultimate request->...)
           */
-         /*
-          * This is the k_pri_req hack. Large numbers of threads
-          * sleeping with kernel priority will cause scheduler thrashing
-          * on an MP machine. This can be seen running Oracle using
-          * directio to ufs files. Sleep at normal priority here to
-          * more closely mimic physio to a device partition. This
-          * workaround is disabled by default as a niced thread could
-          * be starved from running while holding i_rwlock and i_contents.
-          */
-         if (ufs_directio_drop_kpri) {
-                 kpri_req_save = curthread->t_kpri_req;
-                 curthread->t_kpri_req = 0;
-         }
          while ((dbp = tail) != NULL) {
                  tail = dbp->next;
                  newerror = directio_wait_one(dbp, bytes_iop);
                  if (error == 0)
                          error = newerror;
          }
-         if (ufs_directio_drop_kpri)
-                 curthread->t_kpri_req = kpri_req_save;
          return (error);
  }
  /*
   * Initiate direct IO request
   */
--- 220,245 ----