mmc: block: Add write packing control
The write packing control will ensure that read requests latency is
not increased due to long write packed commands.
The trigger for enabling the write packing is managing to pack several
write requests. The number of potential packed requests that will trigger
the packing can be configured via sysfs by writing the required value to:
/sys/block/<block_dev_name>/num_wr_reqs_to_start_packing.
The trigger for disabling the write packing is fetching a read request.
Change-Id: I982170fa6dca9150ea4310bb546b838b7fd30e9b
Signed-off-by: Maya Erez <merez@codeaurora.org>
diff --git a/drivers/mmc/card/queue.c b/drivers/mmc/card/queue.c
index 652e13a..c3a718a 100644
--- a/drivers/mmc/card/queue.c
+++ b/drivers/mmc/card/queue.c
@@ -25,6 +25,13 @@
#define MMC_QUEUE_SUSPENDED (1 << 0)
/*
+ * Based on benchmark tests the default num of requests to trigger the write
+ * packing was determined, to keep the read latency as low as possible and
+ * manage to keep the high write throughput.
+ */
+#define DEFAULT_NUM_REQS_TO_START_PACK 17
+
+/*
* Prepare a MMC request. This just filters out odd stuff.
*/
static int mmc_prep_request(struct request_queue *q, struct request *req)
@@ -193,6 +200,7 @@
mq->mqrq_cur = mqrq_cur;
mq->mqrq_prev = mqrq_prev;
mq->queue->queuedata = mq;
+ mq->num_wr_reqs_to_start_packing = DEFAULT_NUM_REQS_TO_START_PACK;
blk_queue_prep_rq(mq->queue, mmc_prep_request);
queue_flag_set_unlocked(QUEUE_FLAG_NONROT, mq->queue);