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@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
55typedef enum RF_CvscanArmDir_e {
56	rf_cvscan_LEFT,
57	rf_cvscan_RIGHT
58}       RF_CvscanArmDir_t;
59
60typedef 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
73void   *
74rf_CvscanCreate(RF_SectorCount_t sect_per_disk,
75    RF_AllocListElem_t * cl_list, RF_ShutdownList_t ** listp);
76void    rf_CvscanEnqueue(void *qptr, RF_DiskQueueData_t * req, int priority);
77RF_DiskQueueData_t *rf_CvscanDequeue(void *qptr);
78int
79rf_CvscanPromote(void *qptr, RF_StripeNum_t parityStripeID,
80    RF_ReconUnitNum_t which_ru);
81
82#endif				/* !_RF__RF_CVSCAN_H_ */
83