include/linux/elevator.h

   1 #ifndef _LINUX_ELEVATOR_H
   2 #define _LINUX_ELEVATOR_H
   3
   4 #define ELEVATOR_DEBUG
   5
   6 typedef void (elevator_fn) (struct request *, elevator_t *,
   7                             struct list_head *,
   8                             struct list_head *, int);
   9
  10 typedef int (elevator_merge_fn) (request_queue_t *, struct request **,
  11                                  struct buffer_head *, int, int *, int *);
  12
  13 typedef void (elevator_dequeue_fn) (struct request *);
  14
  15 struct elevator_s
  16 {
  17         int sequence;
  18
  19         int read_latency;
  20         int write_latency;
  21         int max_bomb_segments;
  22
  23         unsigned int nr_segments;
  24         int read_pendings;
  25
  26         elevator_fn * elevator_fn;
  27         elevator_merge_fn *elevator_merge_fn;
  28         elevator_dequeue_fn *dequeue_fn;
  29
  30         unsigned int queue_ID;
  31 };
  32
  33 void elevator_noop(struct request *, elevator_t *, struct list_head *, struct list_head *, int);
  34 int elevator_noop_merge(request_queue_t *, struct request **, struct buffer_head *, int, int *, int *);
  35 void elevator_noop_dequeue(struct request *);
  36 void elevator_linus(struct request *, elevator_t *, struct list_head *, struct list_head *, int);
  37 int elevator_linus_merge(request_queue_t *, struct request **, struct buffer_head *, int, int *, int *);
  38
  39 typedef struct blkelv_ioctl_arg_s {
  40         int queue_ID;
  41         int read_latency;
  42         int write_latency;
  43         int max_bomb_segments;
  44 } blkelv_ioctl_arg_t;
  45
  46 #define BLKELVGET   _IOR(0x12,106,sizeof(blkelv_ioctl_arg_t))
  47 #define BLKELVSET   _IOW(0x12,107,sizeof(blkelv_ioctl_arg_t))
  48
  49 extern int blkelvget_ioctl(elevator_t *, blkelv_ioctl_arg_t *);
  50 extern int blkelvset_ioctl(elevator_t *, const blkelv_ioctl_arg_t *);
  51
  52 extern void elevator_init(elevator_t *, elevator_t);
  53
  54 /*
  55  * Return values from elevator merger
  56  */
  57 #define ELEVATOR_NO_MERGE       0
  58 #define ELEVATOR_FRONT_MERGE    1
  59 #define ELEVATOR_BACK_MERGE     2
  60
  61 /*
  62  * This is used in the elevator algorithm.  We don't prioritise reads
  63  * over writes any more --- although reads are more time-critical than
  64  * writes, by treating them equally we increase filesystem throughput.
  65  * This turns out to give better overall performance.  -- sct
  66  */
  67 #define IN_ORDER(s1,s2)                         \
  68         ((((s1)->rq_dev == (s2)->rq_dev &&      \
  69            (s1)->sector < (s2)->sector)) ||     \
  70          (s1)->rq_dev < (s2)->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 ELEVATOR_NOOP                                           \
  84 ((elevator_t) {                                                 \
  85         0,                              /* sequence */          \
  86                                                                 \
  87         0,                              /* read_latency */      \
  88         0,                              /* write_latency */     \
  89         0,                              /* max_bomb_segments */ \
  90                                                                 \
  91         0,                              /* nr_segments */       \
  92         0,                              /* read_pendings */     \
  93                                                                 \
  94         elevator_noop,                  /* elevator_fn */       \
  95         elevator_noop_merge,            /* elevator_merge_fn */ \
  96         elevator_noop_dequeue,          /* dequeue_fn */        \
  97         })
  98
  99 #define ELEVATOR_LINUS                                          \
 100 ((elevator_t) {                                                 \
 101         0,                              /* not used */          \
 102                                                                 \
 103         1000000,                                /* read passovers */    \
 104         2000000,                                /* write passovers */   \
 105         0,                              /* max_bomb_segments */ \
 106                                                                 \
 107         0,                              /* not used */          \
 108         0,                              /* not used */          \
 109                                                                 \
 110         elevator_linus,                 /* elevator_fn */       \
 111         elevator_linus_merge,           /* elevator_merge_fn */ \
 112         elevator_noop_dequeue,          /* dequeue_fn */        \
 113         })
 114
 115 #endif