include/linux/elevator.h

   1 #ifndef _LINUX_ELEVATOR_H
   2 #define _LINUX_ELEVATOR_H
   3
   4 typedef void (elevator_fn) (struct request *, elevator_t *,
   5                             struct list_head *,
   6                             struct list_head *, int);
   7
   8 typedef int (elevator_merge_fn) (request_queue_t *, struct request **, struct list_head *,
   9                                  struct buffer_head *, int, int);
  10
  11 typedef void (elevator_merge_cleanup_fn) (request_queue_t *, struct request *, int);
  12
  13 typedef void (elevator_merge_req_fn) (struct request *, struct request *);
  14
  15 struct elevator_s
  16 {
  17         int read_latency;
  18         int write_latency;
  19
  20         elevator_merge_fn *elevator_merge_fn;
  21         elevator_merge_req_fn *elevator_merge_req_fn;
  22
  23         unsigned int queue_ID;
  24 };
  25
  26 int elevator_noop_merge(request_queue_t *, struct request **, struct list_head *, struct buffer_head *, int, int);
  27 void elevator_noop_merge_cleanup(request_queue_t *, struct request *, int);
  28 void elevator_noop_merge_req(struct request *, struct request *);
  29
  30 int elevator_linus_merge(request_queue_t *, struct request **, struct list_head *, struct buffer_head *, int, int);
  31 void elevator_linus_merge_cleanup(request_queue_t *, struct request *, int);
  32 void elevator_linus_merge_req(struct request *, struct request *);
  33
  34 typedef struct blkelv_ioctl_arg_s {
  35         int queue_ID;
  36         int read_latency;
  37         int write_latency;
  38         int max_bomb_segments;
  39 } blkelv_ioctl_arg_t;
  40
  41 #define BLKELVGET   _IOR(0x12,106,sizeof(blkelv_ioctl_arg_t))
  42 #define BLKELVSET   _IOW(0x12,107,sizeof(blkelv_ioctl_arg_t))
  43
  44 extern int blkelvget_ioctl(elevator_t *, blkelv_ioctl_arg_t *);
  45 extern int blkelvset_ioctl(elevator_t *, const blkelv_ioctl_arg_t *);
  46
  47 extern void elevator_init(elevator_t *, elevator_t);
  48
  49 /*
  50  * Return values from elevator merger
  51  */
  52 #define ELEVATOR_NO_MERGE       0
  53 #define ELEVATOR_FRONT_MERGE    1
  54 #define ELEVATOR_BACK_MERGE     2
  55
  56 /*
  57  * This is used in the elevator algorithm.  We don't prioritise reads
  58  * over writes any more --- although reads are more time-critical than
  59  * writes, by treating them equally we increase filesystem throughput.
  60  * This turns out to give better overall performance.  -- sct
  61  */
  62 #define IN_ORDER(s1,s2)                         \
  63         ((((s1)->rq_dev == (s2)->rq_dev &&      \
  64            (s1)->sector < (s2)->sector)) ||     \
  65          (s1)->rq_dev < (s2)->rq_dev)
  66
  67 #define BHRQ_IN_ORDER(bh, rq)                   \
  68         ((((bh)->b_rdev == (rq)->rq_dev &&      \
  69            (bh)->b_rsector < (rq)->sector)) ||  \
  70          (bh)->b_rdev < (rq)->rq_dev)
  71
  72 static inline int elevator_request_latency(elevator_t * elevator, int rw)
  73 {
  74         int latency;
  75
  76         latency = elevator->read_latency;
  77         if (rw != READ)
  78                 latency = elevator->write_latency;
  79
  80         return latency;
  81 }
  82
  83 #define ELV_LINUS_SEEK_COST     16
  84
  85 #define ELEVATOR_NOOP                                                   \
  86 ((elevator_t) {                                                         \
  87         0,                              /* read_latency */              \
  88         0,                              /* write_latency */             \
  89                                                                         \
  90         elevator_noop_merge,            /* elevator_merge_fn */         \
  91         elevator_noop_merge_req,        /* elevator_merge_req_fn */     \
  92         })
  93
  94 #define ELEVATOR_LINUS                                                  \
  95 ((elevator_t) {                                                         \
  96         2048,                           /* read passovers */            \
  97         8192,                           /* write passovers */           \
  98                                                                         \
  99         elevator_linus_merge,           /* elevator_merge_fn */         \
 100         elevator_linus_merge_req,       /* elevator_merge_req_fn */     \
 101         })
 102
 103 #endif