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row: Add support for urgent request handling

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This patch adds support for handling urgent requests.
ROW queue can be marked as "urgent" so if it was un-served in last
dispatch cycle and a request was added to it - it will trigger
issuing an urgent-request-notification to the block device driver.
The block device driver may choose at stop the transmission of current
ongoing request to handle the urgent one. Foe example: long WRITE may
be stopped to handle an urgent READ. This decreases READ latency.


Change-Id: I84954c13f5e3b1b5caeadc9fe1f9aa21208cb35e
Signed-off-by: Tatyana Brokhman <tlinder@codeaurora.org>
This commit is contained in:
Tatyana Brokhman 2012-12-20 19:23:58 +02:00
parent b7bf9ac0e4
commit 0ef8143596
1 changed files with 41 additions and 1 deletions
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42
block/row-iosched.c
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@ -58,6 +58,17 @@ static const bool queue_idling_enabled[] = {
false, /* ROWQ_PRIO_LOW_SWRITE */
};
/* Flags indicating whether the queue can notify on urgent requests */
static const bool urgent_queues[] = {
true, /* ROWQ_PRIO_HIGH_READ */
true, /* ROWQ_PRIO_REG_READ */
false, /* ROWQ_PRIO_HIGH_SWRITE */
false, /* ROWQ_PRIO_REG_SWRITE */
false, /* ROWQ_PRIO_REG_WRITE */
false, /* ROWQ_PRIO_LOW_READ */
false, /* ROWQ_PRIO_LOW_SWRITE */
};
/* Default values for row queues quantums in each dispatch cycle */
static const int queue_quantum[] = {
100, /* ROWQ_PRIO_HIGH_READ */
@ -269,7 +280,13 @@ static void row_add_request(struct request_queue *q,
rqueue->idle_data.idle_trigger_time =
jiffies + msecs_to_jiffies(rd->read_idle.freq);
}
row_log_rowq(rd, rqueue->prio, "added request");
if (urgent_queues[rqueue->prio] &&
row_rowq_unserved(rd, rqueue->prio)) {
row_log_rowq(rd, rqueue->prio,
"added urgent req curr_queue = %d",
rd->curr_queue);
} else
row_log_rowq(rd, rqueue->prio, "added request");
}
/**
@ -304,6 +321,28 @@ static int row_reinsert_req(struct request_queue *q,
return 0;
}
/**
* row_urgent_pending() - Return TRUE if there is an urgent
* request on scheduler
* @q: requests queue
*/
static bool row_urgent_pending(struct request_queue *q)
{
struct row_data *rd = q->elevator->elevator_data;
int i;
for (i = 0; i < ROWQ_MAX_PRIO; i++)
if (urgent_queues[i] && row_rowq_unserved(rd, i) &&
!list_empty(&rd->row_queues[i].rqueue.fifo)) {
row_log_rowq(rd, i,
"Urgent request pending (curr=%i)",
rd->curr_queue);
return true;
}
return false;
}
/**
* row_remove_request() - Remove given request from scheduler
* @q: requests queue
@ -689,6 +728,7 @@ static struct elevator_type iosched_row = {
.elevator_dispatch_fn = row_dispatch_requests,
.elevator_add_req_fn = row_add_request,
.elevator_reinsert_req_fn = row_reinsert_req,
.elevator_is_urgent_fn = row_urgent_pending,
.elevator_former_req_fn = elv_rb_former_request,
.elevator_latter_req_fn = elv_rb_latter_request,
.elevator_set_req_fn = row_set_request,