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      1 /*	$NetBSD: rf_cvscan.h,v 1.7 2021/07/27 03:09:26 oster Exp $	*/
      2 /*
      3  * Copyright (c) 1995 Carnegie-Mellon University.
      4  * All rights reserved.
      5  *
      6  * Author: Mark Holland
      7  *
      8  * Permission to use, copy, modify and distribute this software and
      9  * its documentation is hereby granted, provided that both the copyright
     10  * notice and this permission notice appear in all copies of the
     11  * software, derivative works or modified versions, and any portions
     12  * thereof, and that both notices appear in supporting documentation.
     13  *
     14  * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
     15  * CONDITION.  CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND
     16  * FOR ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
     17  *
     18  * Carnegie Mellon requests users of this software to return to
     19  *
     20  *  Software Distribution Coordinator  or  Software.Distribution (at) CS.CMU.EDU
     21  *  School of Computer Science
     22  *  Carnegie Mellon University
     23  *  Pittsburgh PA 15213-3890
     24  *
     25  * any improvements or extensions that they make and grant Carnegie the
     26  * rights to redistribute these changes.
     27  */
     28 
     29 /*
     30 **	Disk scheduling by CVSCAN( N, r )
     31 **
     32 **	Given a set of requests, partition them into one set on each
     33 **	side of the current arm position.  The trick is to pick which
     34 **	side you are going to service next; once a side is picked you will
     35 **	service the closest request.
     36 **	Let there be n1 requests on one side and n2 requests on the other
     37 **	side.  If one of n1 or n2 is zero, select the other side.
     38 **	If both n1 and n2 are nonzero, select a "range" for examination
     39 **	that is N' = min( n1, n2, N ).  Average the distance from the
     40 **	current position to the nearest N' requests on each side giving
     41 **	d1 and d2.
     42 **	Suppose the last decision was to move toward set 2, then the
     43 **	current direction is toward set 2, and you will only switch to set
     44 **	1 if d1+R < d2 where R is r*(total number of cylinders), r in [0,1].
     45 **
     46 **	I extend this by applying only to the set of requests that all
     47 **	share the same, highest priority level.
     48 */
     49 
     50 #ifndef _RF__RF_CVSCAN_H_
     51 #define _RF__RF_CVSCAN_H_
     52 
     53 #include "rf_diskqueue.h"
     54 
     55 typedef enum RF_CvscanArmDir_e {
     56 	rf_cvscan_LEFT,
     57 	rf_cvscan_RIGHT
     58 }       RF_CvscanArmDir_t;
     59 
     60 typedef struct RF_CvscanHeader_s {
     61 	long    range_for_avg;	/* CVSCAN param N */
     62 	long    change_penalty;	/* CVSCAN param R */
     63 	RF_CvscanArmDir_t direction;
     64 	RF_SectorNum_t cur_block;
     65 	int     nxt_priority;
     66 	RF_DiskQueueData_t *left;
     67 	int     left_cnt;
     68 	RF_DiskQueueData_t *right;
     69 	int     right_cnt;
     70 	RF_DiskQueueData_t *burner;
     71 }       RF_CvscanHeader_t;
     72 
     73 void   *
     74 rf_CvscanCreate(RF_SectorCount_t sect_per_disk,
     75     RF_AllocListElem_t * cl_list, RF_ShutdownList_t ** listp);
     76 void    rf_CvscanEnqueue(void *qptr, RF_DiskQueueData_t * req, int priority);
     77 RF_DiskQueueData_t *rf_CvscanDequeue(void *qptr);
     78 int
     79 rf_CvscanPromote(void *qptr, RF_StripeNum_t parityStripeID,
     80     RF_ReconUnitNum_t which_ru);
     81 
     82 #endif				/* !_RF__RF_CVSCAN_H_ */
     83