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

     /*      $NetBSD: bufq_readprio.c,v 1.7 2005/12/11 12:24:29 christos Exp $       */
     /*      NetBSD: subr_disk.c,v 1.61 2004/09/25 03:30:44 thorpej Exp      */
     
     /*-
      * Copyright (c) 1996, 1997, 1999, 2000 The NetBSD Foundation, Inc.
      * All rights reserved.
      *
      * This code is derived from software contributed to The NetBSD Foundation
      * by Jason R. Thorpe of the Numerical Aerospace Simulation Facility,
     * NASA Ames Research Center.
     *
     * Redistribution and use in source and binary forms, with or without
     * modification, are permitted provided that the following conditions
     * are met:
     * 1. Redistributions of source code must retain the above copyright
     *    notice, this list of conditions and the following disclaimer.
     * 2. Redistributions in binary form must reproduce the above copyright
     *    notice, this list of conditions and the following disclaimer in the
     *    documentation and/or other materials provided with the distribution.
     * 3. All advertising materials mentioning features or use of this software
     *    must display the following acknowledgement:
     *      This product includes software developed by the NetBSD
     *      Foundation, Inc. and its contributors.
     * 4. Neither the name of The NetBSD Foundation nor the names of its
     *    contributors may be used to endorse or promote products derived
     *    from this software without specific prior written permission.
     *
     * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
     * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
     * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
     * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
     * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
     * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
     * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
     * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
     * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
     * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
     * POSSIBILITY OF SUCH DAMAGE.
     */
    
    /*
     * Copyright (c) 1982, 1986, 1988, 1993
     *      The Regents of the University of California.  All rights reserved.
     * (c) UNIX System Laboratories, Inc.
     * All or some portions of this file are derived from material licensed
     * to the University of California by American Telephone and Telegraph
     * Co. or Unix System Laboratories, Inc. and are reproduced herein with
     * the permission of UNIX System Laboratories, Inc.
     *
     * Redistribution and use in source and binary forms, with or without
     * modification, are permitted provided that the following conditions
     * are met:
     * 1. Redistributions of source code must retain the above copyright
     *    notice, this list of conditions and the following disclaimer.
     * 2. Redistributions in binary form must reproduce the above copyright
     *    notice, this list of conditions and the following disclaimer in the
     *    documentation and/or other materials provided with the distribution.
     * 3. Neither the name of the University nor the names of its contributors
     *    may be used to endorse or promote products derived from this software
     *    without specific prior written permission.
     *
     * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
     * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
     * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     * SUCH DAMAGE.
     *
     *      @(#)ufs_disksubr.c      8.5 (Berkeley) 1/21/94
     */
    
    #include <sys/cdefs.h>
    __KERNEL_RCSID(0, "$NetBSD: bufq_readprio.c,v 1.7 2005/12/11 12:24:29 christos Exp $");
    
    #include <sys/param.h>
    #include <sys/systm.h>
    #include <sys/buf.h>
    #include <sys/bufq.h>
    #include <sys/bufq_impl.h>
    #include <sys/malloc.h>
    
    /*
     * Seek sort for disks.
     *
     * There are two queues.  The first queue holds read requests; the second
     * holds write requests.  The read queue is first-come first-served; the
     * write queue is sorted in ascendening block order.
     * The read queue is processed first.  After PRIO_READ_BURST consecutive
     * read requests with non-empty write queue PRIO_WRITE_REQ requests from
     * the write queue will be processed.
     */
    
    #define PRIO_READ_BURST         48
    #define PRIO_WRITE_REQ          16
   
   struct bufq_prio {
           TAILQ_HEAD(, buf) bq_read, bq_write; /* actual list of buffers */
           struct buf *bq_write_next;      /* next request in bq_write */
           struct buf *bq_next;            /* current request */
           int bq_read_burst;              /* # of consecutive reads */
   };
   
   static void bufq_readprio_init(struct bufq_state *);
   static void bufq_prio_put(struct bufq_state *, struct buf *);
   static struct buf *bufq_prio_get(struct bufq_state *, int);
   
   BUFQ_DEFINE(readprio, 30, bufq_readprio_init);
   
   static void
   bufq_prio_put(struct bufq_state *bufq, struct buf *bp)
   {
           struct bufq_prio *prio = bufq->bq_private;
           struct buf *bq;
           int sortby;
   
           sortby = bufq->bq_flags & BUFQ_SORT_MASK;
   
           /*
            * If it's a read request append it to the list.
            */
           if ((bp->b_flags & B_READ) == B_READ) {
                   TAILQ_INSERT_TAIL(&prio->bq_read, bp, b_actq);
                   return;
           }
   
           bq = TAILQ_FIRST(&prio->bq_write);
   
           /*
            * If the write list is empty, simply append it to the list.
            */
           if (bq == NULL) {
                   TAILQ_INSERT_TAIL(&prio->bq_write, bp, b_actq);
                   prio->bq_write_next = bp;
                   return;
           }
   
           /*
            * If we lie after the next request, insert after this request.
            */
           if (buf_inorder(prio->bq_write_next, bp, sortby))
                   bq = prio->bq_write_next;
   
           /*
            * Search for the first request at a larger block number.
            * We go before this request if it exists.
            */
           while (bq != NULL && buf_inorder(bq, bp, sortby))
                   bq = TAILQ_NEXT(bq, b_actq);
   
           if (bq != NULL)
                   TAILQ_INSERT_BEFORE(bq, bp, b_actq);
           else
                   TAILQ_INSERT_TAIL(&prio->bq_write, bp, b_actq);
   }
   
   static struct buf *
   bufq_prio_get(struct bufq_state *bufq, int remove)
   {
           struct bufq_prio *prio = bufq->bq_private;
           struct buf *bp;
   
           /*
            * If no current request, get next from the lists.
            */
           if (prio->bq_next == NULL) {
                   /*
                    * If at least one list is empty, select the other.
                    */
                   if (TAILQ_FIRST(&prio->bq_read) == NULL) {
                           prio->bq_next = prio->bq_write_next;
                           prio->bq_read_burst = 0;
                   } else if (prio->bq_write_next == NULL) {
                           prio->bq_next = TAILQ_FIRST(&prio->bq_read);
                           prio->bq_read_burst = 0;
                   } else {
                           /*
                            * Both list have requests.  Select the read list up
                            * to PRIO_READ_BURST times, then select the write
                            * list PRIO_WRITE_REQ times.
                            */
                           if (prio->bq_read_burst++ < PRIO_READ_BURST)
                                   prio->bq_next = TAILQ_FIRST(&prio->bq_read);
                           else if (prio->bq_read_burst <
                               PRIO_READ_BURST + PRIO_WRITE_REQ)
                                   prio->bq_next = prio->bq_write_next;
                           else {
                                   prio->bq_next = TAILQ_FIRST(&prio->bq_read);
                                   prio->bq_read_burst = 0;
                           }
                   }
           }
   
           bp = prio->bq_next;
   
           if (bp != NULL && remove) {
                   if ((bp->b_flags & B_READ) == B_READ)
                           TAILQ_REMOVE(&prio->bq_read, bp, b_actq);
                   else {
                           /*
                            * Advance the write pointer before removing
                            * bp since it is actually prio->bq_write_next.
                            */
                           prio->bq_write_next =
                               TAILQ_NEXT(prio->bq_write_next, b_actq);
                           TAILQ_REMOVE(&prio->bq_write, bp, b_actq);
                           if (prio->bq_write_next == NULL)
                                   prio->bq_write_next =
                                       TAILQ_FIRST(&prio->bq_write);
                   }
   
                   prio->bq_next = NULL;
           }
   
           return (bp);
   }
   
   static void
   bufq_readprio_init(struct bufq_state *bufq)
   {
           struct bufq_prio *prio;
   
           bufq->bq_get = bufq_prio_get;
           bufq->bq_put = bufq_prio_put;
           bufq->bq_private = malloc(sizeof(struct bufq_prio), M_DEVBUF, M_ZERO);
           prio = (struct bufq_prio *)bufq->bq_private;
           TAILQ_INIT(&prio->bq_read);
           TAILQ_INIT(&prio->bq_write);
   }
   

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