block: Add API for urgent request handling
This patch add support in block & elevator layers for handling
urgent requests. The decision if a request is urgent or not is taken
by the scheduler. Urgent request notification is passed to the underlying
block device driver (eMMC for example). Block device driver may decide to
interrupt the currently running low priority request to serve the new
urgent request. By doing so READ latency is greatly reduced in read&write
collision scenarios.
Note that if the current scheduler doesn't implement the urgent request
mechanism, this code path is never activated.
Change-Id: I8aa74b9b45c0d3a2221bd4e82ea76eb4103e7cfa
Signed-off-by: Tatyana Brokhman <tlinder@codeaurora.org>
diff --git a/block/blk-settings.c b/block/blk-settings.c
index d3234fc..579328c 100644
--- a/block/blk-settings.c
+++ b/block/blk-settings.c
@@ -100,6 +100,18 @@
EXPORT_SYMBOL_GPL(blk_queue_lld_busy);
/**
+ * blk_urgent_request() - Set an urgent_request handler function for queue
+ * @q: queue
+ * @fn: handler for urgent requests
+ *
+ */
+void blk_urgent_request(struct request_queue *q, request_fn_proc *fn)
+{
+ q->urgent_request_fn = fn;
+}
+EXPORT_SYMBOL(blk_urgent_request);
+
+/**
* blk_set_default_limits - reset limits to default values
* @lim: the queue_limits structure to reset
*