The Design and Implementation of the FreeBSD Operating System, Second Edition
Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)


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FreeBSD/Linux Kernel Cross Reference
sys/kern/bufq_readprio.c

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    1 /*      $NetBSD: bufq_readprio.c,v 1.16 2017/05/04 11:03:27 kamil Exp $ */
    2 /*      NetBSD: subr_disk.c,v 1.61 2004/09/25 03:30:44 thorpej Exp      */
    3 
    4 /*-
    5  * Copyright (c) 1996, 1997, 1999, 2000 The NetBSD Foundation, Inc.
    6  * All rights reserved.
    7  *
    8  * This code is derived from software contributed to The NetBSD Foundation
    9  * by Jason R. Thorpe of the Numerical Aerospace Simulation Facility,
   10  * NASA Ames Research Center.
   11  *
   12  * Redistribution and use in source and binary forms, with or without
   13  * modification, are permitted provided that the following conditions
   14  * are met:
   15  * 1. Redistributions of source code must retain the above copyright
   16  *    notice, this list of conditions and the following disclaimer.
   17  * 2. Redistributions in binary form must reproduce the above copyright
   18  *    notice, this list of conditions and the following disclaimer in the
   19  *    documentation and/or other materials provided with the distribution.
   20  *
   21  * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
   22  * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
   23  * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
   24  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
   25  * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
   26  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
   27  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
   28  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
   29  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
   30  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
   31  * POSSIBILITY OF SUCH DAMAGE.
   32  */
   33 
   34 /*
   35  * Copyright (c) 1982, 1986, 1988, 1993
   36  *      The Regents of the University of California.  All rights reserved.
   37  * (c) UNIX System Laboratories, Inc.
   38  * All or some portions of this file are derived from material licensed
   39  * to the University of California by American Telephone and Telegraph
   40  * Co. or Unix System Laboratories, Inc. and are reproduced herein with
   41  * the permission of UNIX System Laboratories, Inc.
   42  *
   43  * Redistribution and use in source and binary forms, with or without
   44  * modification, are permitted provided that the following conditions
   45  * are met:
   46  * 1. Redistributions of source code must retain the above copyright
   47  *    notice, this list of conditions and the following disclaimer.
   48  * 2. Redistributions in binary form must reproduce the above copyright
   49  *    notice, this list of conditions and the following disclaimer in the
   50  *    documentation and/or other materials provided with the distribution.
   51  * 3. Neither the name of the University nor the names of its contributors
   52  *    may be used to endorse or promote products derived from this software
   53  *    without specific prior written permission.
   54  *
   55  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
   56  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   57  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   58  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
   59  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   60  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   61  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   62  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   63  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   64  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   65  * SUCH DAMAGE.
   66  *
   67  *      @(#)ufs_disksubr.c      8.5 (Berkeley) 1/21/94
   68  */
   69 
   70 #include <sys/cdefs.h>
   71 __KERNEL_RCSID(0, "$NetBSD: bufq_readprio.c,v 1.16 2017/05/04 11:03:27 kamil Exp $");
   72 
   73 #include <sys/param.h>
   74 #include <sys/systm.h>
   75 #include <sys/buf.h>
   76 #include <sys/bufq.h>
   77 #include <sys/bufq_impl.h>
   78 #include <sys/kmem.h>
   79 #include <sys/module.h>
   80 
   81 /*
   82  * Seek sort for disks.
   83  *
   84  * There are two queues.  The first queue holds read requests; the second
   85  * holds write requests.  The read queue is first-come first-served; the
   86  * write queue is sorted in ascendening block order.
   87  * The read queue is processed first.  After PRIO_READ_BURST consecutive
   88  * read requests with non-empty write queue PRIO_WRITE_REQ requests from
   89  * the write queue will be processed.
   90  */
   91 
   92 #define PRIO_READ_BURST         48
   93 #define PRIO_WRITE_REQ          16
   94 
   95 struct bufq_prio {
   96         TAILQ_HEAD(, buf) bq_read, bq_write; /* actual list of buffers */
   97         struct buf *bq_write_next;      /* next request in bq_write */
   98         struct buf *bq_next;            /* current request */
   99         int bq_read_burst;              /* # of consecutive reads */
  100 };
  101 
  102 static void bufq_readprio_init(struct bufq_state *);
  103 static void bufq_prio_put(struct bufq_state *, struct buf *);
  104 static struct buf *bufq_prio_get(struct bufq_state *, int);
  105 
  106 BUFQ_DEFINE(readprio, 30, bufq_readprio_init);
  107 
  108 static void
  109 bufq_prio_put(struct bufq_state *bufq, struct buf *bp)
  110 {
  111         struct bufq_prio *prio = bufq_private(bufq);
  112         struct buf *bq;
  113         int sortby;
  114 
  115         sortby = bufq->bq_flags & BUFQ_SORT_MASK;
  116 
  117         /*
  118          * If it's a read request append it to the list.
  119          */
  120         if ((bp->b_flags & B_READ) == B_READ) {
  121                 TAILQ_INSERT_TAIL(&prio->bq_read, bp, b_actq);
  122                 return;
  123         }
  124 
  125         bq = TAILQ_FIRST(&prio->bq_write);
  126 
  127         /*
  128          * If the write list is empty, simply append it to the list.
  129          */
  130         if (bq == NULL) {
  131                 TAILQ_INSERT_TAIL(&prio->bq_write, bp, b_actq);
  132                 prio->bq_write_next = bp;
  133                 return;
  134         }
  135 
  136         /*
  137          * If we lie after the next request, insert after this request.
  138          */
  139         if (buf_inorder(prio->bq_write_next, bp, sortby))
  140                 bq = prio->bq_write_next;
  141 
  142         /*
  143          * Search for the first request at a larger block number.
  144          * We go before this request if it exists.
  145          */
  146         while (bq != NULL && buf_inorder(bq, bp, sortby))
  147                 bq = TAILQ_NEXT(bq, b_actq);
  148 
  149         if (bq != NULL)
  150                 TAILQ_INSERT_BEFORE(bq, bp, b_actq);
  151         else
  152                 TAILQ_INSERT_TAIL(&prio->bq_write, bp, b_actq);
  153 }
  154 
  155 static struct buf *
  156 bufq_prio_get(struct bufq_state *bufq, int remove)
  157 {
  158         struct bufq_prio *prio = bufq_private(bufq);
  159         struct buf *bp;
  160 
  161         /*
  162          * If no current request, get next from the lists.
  163          */
  164         if (prio->bq_next == NULL) {
  165                 /*
  166                  * If at least one list is empty, select the other.
  167                  */
  168                 if (TAILQ_FIRST(&prio->bq_read) == NULL) {
  169                         prio->bq_next = prio->bq_write_next;
  170                         prio->bq_read_burst = 0;
  171                 } else if (prio->bq_write_next == NULL) {
  172                         bp = prio->bq_next = TAILQ_FIRST(&prio->bq_read);
  173                         prio->bq_read_burst = 0;
  174                         KASSERT((bp == NULL) ||
  175                             ((bp->b_flags & B_READ) == B_READ));
  176                 } else {
  177                         /*
  178                          * Both list have requests.  Select the read list up
  179                          * to PRIO_READ_BURST times, then select the write
  180                          * list PRIO_WRITE_REQ times.
  181                          */
  182                         if (prio->bq_read_burst++ < PRIO_READ_BURST)
  183                                 prio->bq_next = TAILQ_FIRST(&prio->bq_read);
  184                         else if (prio->bq_read_burst <
  185                             PRIO_READ_BURST + PRIO_WRITE_REQ)
  186                                 prio->bq_next = prio->bq_write_next;
  187                         else {
  188                                 prio->bq_next = TAILQ_FIRST(&prio->bq_read);
  189                                 prio->bq_read_burst = 0;
  190                         }
  191                 }
  192         }
  193 
  194         bp = prio->bq_next;
  195 
  196         if (bp != NULL && remove) {
  197                 if ((bp->b_flags & B_READ) == B_READ)
  198                         TAILQ_REMOVE(&prio->bq_read, bp, b_actq);
  199                 else {
  200                         /*
  201                          * Advance the write pointer before removing
  202                          * bp since it is actually prio->bq_write_next.
  203                          */
  204                         prio->bq_write_next =
  205                             TAILQ_NEXT(prio->bq_write_next, b_actq);
  206                         TAILQ_REMOVE(&prio->bq_write, bp, b_actq);
  207                         if (prio->bq_write_next == NULL)
  208                                 prio->bq_write_next =
  209                                     TAILQ_FIRST(&prio->bq_write);
  210                 }
  211 
  212                 prio->bq_next = NULL;
  213         }
  214 
  215         return (bp);
  216 }
  217 
  218 static struct buf *
  219 bufq_prio_cancel(struct bufq_state *bufq, struct buf *buf)
  220 {
  221         struct bufq_prio *prio = bufq_private(bufq);
  222         struct buf *bq;
  223 
  224         /* search read queue */
  225         TAILQ_FOREACH(bq, &prio->bq_read, b_actq) {
  226                 if (bq == buf) {
  227                         TAILQ_REMOVE(&prio->bq_read, bq, b_actq);
  228                         /* force new section */
  229                         prio->bq_next = NULL;
  230                         return buf;
  231                 }
  232         }
  233 
  234         /* not found in read queue, search write queue */
  235         TAILQ_FOREACH(bq, &prio->bq_write, b_actq) {
  236                 if (bq == buf) {
  237                         if (bq == prio->bq_write_next) {
  238                                 /*
  239                                  * Advance the write pointer before removing
  240                                  * bp since it is actually prio->bq_write_next.
  241                                  */
  242                                 prio->bq_write_next =
  243                                     TAILQ_NEXT(prio->bq_write_next, b_actq);
  244                                 TAILQ_REMOVE(&prio->bq_write, bq, b_actq);
  245                                 if (prio->bq_write_next == NULL)
  246                                         prio->bq_write_next =
  247                                             TAILQ_FIRST(&prio->bq_write);
  248                         } else {
  249                                 TAILQ_REMOVE(&prio->bq_write, bq, b_actq);
  250                         }
  251                         /* force new section */
  252                         prio->bq_next = NULL;
  253                         return buf;
  254                 }
  255         }
  256 
  257         /* still not found */
  258         return NULL;
  259 }
  260 
  261 static void
  262 bufq_prio_fini(struct bufq_state *bufq)
  263 {
  264 
  265         KASSERT(bufq->bq_private != NULL);
  266         kmem_free(bufq->bq_private, sizeof(struct bufq_prio));
  267 }
  268 
  269 static void
  270 bufq_readprio_init(struct bufq_state *bufq)
  271 {
  272         struct bufq_prio *prio;
  273 
  274         bufq->bq_get = bufq_prio_get;
  275         bufq->bq_put = bufq_prio_put;
  276         bufq->bq_cancel = bufq_prio_cancel;
  277         bufq->bq_fini = bufq_prio_fini;
  278         bufq->bq_private = kmem_zalloc(sizeof(struct bufq_prio), KM_SLEEP);
  279         prio = (struct bufq_prio *)bufq->bq_private;
  280         TAILQ_INIT(&prio->bq_read);
  281         TAILQ_INIT(&prio->bq_write);
  282 }
  283 
  284 MODULE(MODULE_CLASS_BUFQ, bufq_readprio, NULL);
  285  
  286 static int 
  287 bufq_readprio_modcmd(modcmd_t cmd, void *opaque)
  288 {
  289  
  290         switch (cmd) {
  291         case MODULE_CMD_INIT: 
  292                 return bufq_register(&bufq_strat_readprio);
  293         case MODULE_CMD_FINI:
  294                 return bufq_unregister(&bufq_strat_readprio);
  295         default:
  296                 return ENOTTY;
  297         }
  298 }

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