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    Subject[PATCH 2/7] iosched: introduce parameter deadline.reada_expire
    Introduce parameter reada_expire to the deadline elevator.

    It avoids readahead requests contending with read requests,
    and helps improve latency/throughput when there's many concurrent readers.

    Signed-off-by: Wu Fengguang <wfg@mail.ustc.edu.cn>
    ---


    --- linux-2.6.17-rc6-mm2.orig/block/deadline-iosched.c
    +++ linux-2.6.17-rc6-mm2/block/deadline-iosched.c
    @@ -19,7 +19,8 @@
    /*
    * See Documentation/block/deadline-iosched.txt
    */
    -static const int read_expire = HZ / 2; /* max time before a read is submitted. */
    +static const int read_expire = HZ / 2; /* max time before an _impending_ read is submitted. */
    +static const int reada_expire = 60 * HZ;/* max time before a read-ahead is submitted. */
    static const int write_expire = 5 * HZ; /* ditto for writes, these limits are SOFT! */
    static const int writes_starved = 2; /* max times reads can starve a write */
    static const int fifo_batch = 16; /* # of sequential requests treated as one
    @@ -56,7 +57,7 @@ struct deadline_data {
    /*
    * settings that change how the i/o scheduler behaves
    */
    - int fifo_expire[2];
    + int fifo_expire[4];
    int fifo_batch;
    int writes_starved;
    int front_merges;
    @@ -711,7 +712,9 @@ static void *deadline_init_queue(request
    dd->sort_list[READ] = RB_ROOT;
    dd->sort_list[WRITE] = RB_ROOT;
    dd->fifo_expire[READ] = read_expire;
    + dd->fifo_expire[READA] = reada_expire;
    dd->fifo_expire[WRITE] = write_expire;
    + dd->fifo_expire[WRITEA] = write_expire;
    dd->writes_starved = writes_starved;
    dd->front_merges = 1;
    dd->fifo_batch = fifo_batch;
    @@ -780,6 +783,7 @@ static ssize_t __FUNC(elevator_t *e, cha
    return deadline_var_show(__data, (page)); \
    }
    SHOW_FUNCTION(deadline_read_expire_show, dd->fifo_expire[READ], 1);
    +SHOW_FUNCTION(deadline_reada_expire_show, dd->fifo_expire[READA], 1);
    SHOW_FUNCTION(deadline_write_expire_show, dd->fifo_expire[WRITE], 1);
    SHOW_FUNCTION(deadline_writes_starved_show, dd->writes_starved, 0);
    SHOW_FUNCTION(deadline_front_merges_show, dd->front_merges, 0);
    @@ -803,6 +807,7 @@ static ssize_t __FUNC(elevator_t *e, con
    return ret; \
    }
    STORE_FUNCTION(deadline_read_expire_store, &dd->fifo_expire[READ], 0, INT_MAX, 1);
    +STORE_FUNCTION(deadline_reada_expire_store, &dd->fifo_expire[READA], 0, INT_MAX, 1);
    STORE_FUNCTION(deadline_write_expire_store, &dd->fifo_expire[WRITE], 0, INT_MAX, 1);
    STORE_FUNCTION(deadline_writes_starved_store, &dd->writes_starved, INT_MIN, INT_MAX, 0);
    STORE_FUNCTION(deadline_front_merges_store, &dd->front_merges, 0, 1, 0);
    @@ -815,6 +820,7 @@ STORE_FUNCTION(deadline_fifo_batch_store

    static struct elv_fs_entry deadline_attrs[] = {
    DD_ATTR(read_expire),
    + DD_ATTR(reada_expire),
    DD_ATTR(write_expire),
    DD_ATTR(writes_starved),
    DD_ATTR(front_merges),
    --
    -
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