mmc: add dynamic trigger for packed control
In the current implementation packing is enabled according to a statically
defined trigger. This patch updates the packing control mechanism to use a
dynamically defined trigger.
The trigger's value is calculated by the relation
between the number of potential packed write requests and the mean
value of all previous potential values:
If the current potential is greater than the mean potential then
the heuristic is that the following workload will contain many write
requests, therefore we lower the packed trigger. In the opposite case
we want to increase the trigger in order to get less packing events.
In case we get an urgent request we 'punish' the packing control by
increasing the trigger.
Change-Id: I775e1582ad32a8f798e8b2bd2b3178aef357e747
Signed-off-by: Lee Susman <lsusman@codeaurora.org>
diff --git a/drivers/mmc/card/block.c b/drivers/mmc/card/block.c
index a236425..b82e8df 100644
--- a/drivers/mmc/card/block.c
+++ b/drivers/mmc/card/block.c
@@ -68,6 +68,7 @@
(rq_data_dir(req) == WRITE))
#define PACKED_CMD_VER 0x01
#define PACKED_CMD_WR 0x02
+#define PACKED_TRIGGER_MAX_ELEMENTS 5000
#define MMC_BLK_UPDATE_STOP_REASON(stats, reason) \
do { \
@@ -75,6 +76,12 @@
stats->pack_stop_reason[reason]++; \
} while (0)
+#define PCKD_TRGR_INIT_MEAN_POTEN 17
+#define PCKD_TRGR_POTEN_LOWER_BOUND 5
+#define PCKD_TRGR_URGENT_PENALTY 2
+#define PCKD_TRGR_LOWER_BOUND 5
+#define PCKD_TRGR_PRECISION_MULTIPLIER 100
+
static DEFINE_MUTEX(block_mutex);
/*
@@ -2203,6 +2210,80 @@
}
EXPORT_SYMBOL(mmc_blk_disable_wr_packing);
+static int get_packed_trigger(int potential, struct mmc_card *card,
+ struct request *req, int curr_trigger)
+{
+ static int num_mean_elements = 1;
+ static unsigned long mean_potential = PCKD_TRGR_INIT_MEAN_POTEN;
+ unsigned int trigger = curr_trigger;
+ unsigned int pckd_trgr_upper_bound = card->ext_csd.max_packed_writes;
+
+ /* scale down the upper bound to 75% */
+ pckd_trgr_upper_bound = (pckd_trgr_upper_bound * 3) / 4;
+
+ /*
+ * since the most common calls for this function are with small
+ * potential write values and since we don't want these calls to affect
+ * the packed trigger, set a lower bound and ignore calls with
+ * potential lower than that bound
+ */
+ if (potential <= PCKD_TRGR_POTEN_LOWER_BOUND)
+ return trigger;
+
+ /*
+ * this is to prevent integer overflow in the following calculation:
+ * once every PACKED_TRIGGER_MAX_ELEMENTS reset the algorithm
+ */
+ if (num_mean_elements > PACKED_TRIGGER_MAX_ELEMENTS) {
+ num_mean_elements = 1;
+ mean_potential = PCKD_TRGR_INIT_MEAN_POTEN;
+ }
+
+ /*
+ * get next mean value based on previous mean value and current
+ * potential packed writes. Calculation is as follows:
+ * mean_pot[i+1] =
+ * ((mean_pot[i] * num_mean_elem) + potential)/(num_mean_elem + 1)
+ */
+ mean_potential *= num_mean_elements;
+ /*
+ * add num_mean_elements so that the division of two integers doesn't
+ * lower mean_potential too much
+ */
+ if (potential > mean_potential)
+ mean_potential += num_mean_elements;
+ mean_potential += potential;
+ /* this is for gaining more precision when dividing two integers */
+ mean_potential *= PCKD_TRGR_PRECISION_MULTIPLIER;
+ /* this completes the mean calculation */
+ mean_potential /= ++num_mean_elements;
+ mean_potential /= PCKD_TRGR_PRECISION_MULTIPLIER;
+
+ /*
+ * if current potential packed writes is greater than the mean potential
+ * then the heuristic is that the following workload will contain many
+ * write requests, therefore we lower the packed trigger. In the
+ * opposite case we want to increase the trigger in order to get less
+ * packing events.
+ */
+ if (potential >= mean_potential)
+ trigger = (trigger <= PCKD_TRGR_LOWER_BOUND) ?
+ PCKD_TRGR_LOWER_BOUND : trigger - 1;
+ else
+ trigger = (trigger >= pckd_trgr_upper_bound) ?
+ pckd_trgr_upper_bound : trigger + 1;
+
+ /*
+ * an urgent read request indicates a packed list being interrupted
+ * by this read, therefore we aim for less packing, hence the trigger
+ * gets increased
+ */
+ if (req && (req->cmd_flags & REQ_URGENT) && (rq_data_dir(req) == READ))
+ trigger += PCKD_TRGR_URGENT_PENALTY;
+
+ return trigger;
+}
+
static void mmc_blk_write_packing_control(struct mmc_queue *mq,
struct request *req)
{
@@ -2230,6 +2311,10 @@
if (mq->num_of_potential_packed_wr_reqs >
mq->num_wr_reqs_to_start_packing)
mq->wr_packing_enabled = true;
+ mq->num_wr_reqs_to_start_packing =
+ get_packed_trigger(mq->num_of_potential_packed_wr_reqs,
+ mq->card, req,
+ mq->num_wr_reqs_to_start_packing);
mq->num_of_potential_packed_wr_reqs = 0;
return;
}
@@ -2238,6 +2323,12 @@
if (data_dir == READ) {
mmc_blk_disable_wr_packing(mq);
+ mq->num_wr_reqs_to_start_packing =
+ get_packed_trigger(mq->num_of_potential_packed_wr_reqs,
+ mq->card, req,
+ mq->num_wr_reqs_to_start_packing);
+ mq->num_of_potential_packed_wr_reqs = 0;
+ mq->wr_packing_enabled = false;
return;
} else if (data_dir == WRITE) {
mq->num_of_potential_packed_wr_reqs++;