row: Add support for urgent request handling
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>
diff --git a/block/row-iosched.c b/block/row-iosched.c
index 583e75b..f1cb619 100644
--- a/block/row-iosched.c
+++ b/block/row-iosched.c
@@ -58,6 +58,17 @@
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 @@
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");
}
/**
@@ -305,6 +322,28 @@
}
/**
+ * 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
* @rq: request to remove
@@ -689,6 +728,7 @@
.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,