linux-2.4.20-new_IO_scheduler.patch

   1 diff -u -ur linux-2.4.20/drivers/block/elevator.c linux-iosched-2/drivers/block/elevator.c
   2 --- linux-2.4.20/drivers/block/elevator.c       2003-04-14 14:47:22.000000000 -0400
   3 +++ linux-iosched-2/drivers/block/elevator.c    2003-05-30 17:28:57.000000000 -0400
   4 @@ -74,6 +74,81 @@
   5         return 0;
   6  }
   7
   8 +int elevator_neil_merge(request_queue_t *q, struct request **req,
   9 +                        struct list_head * head,
  10 +                        struct buffer_head *bh, int rw,
  11 +                        int max_sectors)
  12 +{
  13 +       struct list_head *entry = &q->queue_head;
  14 +       struct request *__rq;
  15 +       unsigned int count = bh->b_size >> 9, ret = ELEVATOR_NO_MERGE;
  16 +       unsigned int reads = 0, writes = 0;
  17 +       /* XXX make tunable? */
  18 +       unsigned int expire_time = jiffies - 1*HZ;
  19 +
  20 +       if (list_empty(&q->queue_head))
  21 +               goto out;
  22 +
  23 +       /* try to merge requests, fall back to ordering them by sector */
  24 +       while ((entry = entry->prev) != head) {
  25 +               __rq = blkdev_entry_to_request(entry);
  26 +
  27 +               if (__rq->elevator_sequence <= 0)
  28 +                       break;
  29 +               if (__rq->cmd == READ)
  30 +                       ++reads;
  31 +               else
  32 +                       ++writes;
  33 +               if (__rq->rq_dev != bh->b_rdev)
  34 +                       continue;
  35 +               if (__rq->waiting)
  36 +                       continue;
  37 +               if (__rq->cmd != rw)
  38 +                       continue;
  39 +               if (time_before(__rq->start_time, expire_time))
  40 +                       break;
  41 +               if (bh->b_rsector > __rq->sector)
  42 +                       *req = __rq;
  43 +               if (__rq->nr_sectors + count > max_sectors)
  44 +                       continue;
  45 +               if (__rq->sector + __rq->nr_sectors == bh->b_rsector) {
  46 +                       ret = ELEVATOR_BACK_MERGE;
  47 +                       *req = __rq;
  48 +                       goto out;
  49 +               } else if (__rq->sector - count == bh->b_rsector) {
  50 +                       ret = ELEVATOR_FRONT_MERGE;
  51 +                       *req = __rq;
  52 +                       goto out;
  53 +               }
  54 +       }
  55 +       if (!*req && rw == READ) {
  56 +               int extra_writes = writes - reads;
  57 +               /*
  58 +                * If there are more writes than reads in the queue then put
  59 +                * read requests ahead of the extra writes.  This prevents
  60 +                * writes from starving reads.
  61 +                */
  62 +               entry = q->queue_head.prev;
  63 +               while (extra_writes > 0 && entry != head) {
  64 +                       __rq = blkdev_entry_to_request(entry);
  65 +                       if (__rq->cmd == WRITE)
  66 +                               --extra_writes;
  67 +                       else if (time_before(__rq->start_time, expire_time))
  68 +                               break;
  69 +                       entry = entry->prev;
  70 +               }
  71 +               *req = blkdev_entry_to_request(entry);
  72 +       }
  73 +out:
  74 +       return ret;
  75 +}
  76 +
  77 +void elevator_neil_merge_req(struct request *req, struct request *next)
  78 +{
  79 +       if (time_before(next->start_time, req->start_time))
  80 +               req->start_time = next->start_time;
  81 +}
  82 +
  83
  84  int elevator_linus_merge(request_queue_t *q, struct request **req,
  85                          struct list_head * head,
  86 diff -u -ur linux-2.4.20/drivers/block/ll_rw_blk.c linux-iosched-2/drivers/block/ll_rw_blk.c
  87 --- linux-2.4.20/drivers/block/ll_rw_blk.c      2003-04-14 14:47:22.000000000 -0400
  88 +++ linux-iosched-2/drivers/block/ll_rw_blk.c   2003-05-30 17:27:16.000000000 -0400
  89 @@ -480,7 +480,7 @@
  90  void blk_init_queue(request_queue_t * q, request_fn_proc * rfn)
  91  {
  92         INIT_LIST_HEAD(&q->queue_head);
  93 -       elevator_init(&q->elevator, ELEVATOR_LINUS);
  94 +       elevator_init(&q->elevator, ELEVATOR_NEIL);
  95         blk_init_free_list(q);
  96         q->request_fn           = rfn;
  97         q->back_merge_fn        = ll_back_merge_fn;
  98 @@ -922,7 +922,8 @@
  99                         rw = READ;      /* drop into READ */
 100                 case READ:
 101                 case WRITE:
 102 -                       latency = elevator_request_latency(elevator, rw);
 103 +                       /* latency = elevator_request_latency(elevator, rw); */
 104 +                       latency = 1;
 105                         break;
 106                 default:
 107                         BUG();
 108 diff -u -ur linux-2.4.20/include/linux/elevator.h linux-iosched-2/include/linux/elevator.h
 109 --- linux-2.4.20/include/linux/elevator.h       2003-04-14 14:47:24.000000000 -0400
 110 +++ linux-iosched-2/include/linux/elevator.h    2003-05-30 17:27:16.000000000 -0400
 111 @@ -31,6 +31,9 @@
 112  void elevator_linus_merge_cleanup(request_queue_t *, struct request *, int);
 113  void elevator_linus_merge_req(struct request *, struct request *);
 114
 115 +int elevator_neil_merge(request_queue_t *, struct request **, struct list_head *, struct buffer_head *, int, int);
 116 +void elevator_neil_merge_req(struct request *, struct request *);
 117 +
 118  typedef struct blkelv_ioctl_arg_s {
 119         int queue_ID;
 120         int read_latency;
 121 @@ -101,3 +104,12 @@
 122         })
 123
 124  #endif
 125 +
 126 +#define ELEVATOR_NEIL                                                  \
 127 +((elevator_t) {                                                                \
 128 +       0,                              /* read_latency */              \
 129 +       0,                              /* write_latency */             \
 130 +                                                                       \
 131 +       elevator_neil_merge,            /* elevator_merge_fn */         \
 132 +       elevator_neil_merge_req,        /* elevator_merge_req_fn */     \
 133 +       })
 134