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/elevator.c b/block/elevator.c
index 737d5dd..efec457 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -814,6 +814,11 @@
{
struct elevator_queue *e = q->elevator;
+ if (test_bit(REQ_ATOM_URGENT, &rq->atomic_flags)) {
+ q->notified_urgent = false;
+ q->dispatched_urgent = false;
+ blk_clear_rq_urgent(rq);
+ }
/*
* request is released from the driver, io must be done
*/