[PATCH v1 0/1] mmc: block: Add write packing control

[PATCH v1 0/1] mmc: block: Add write packing control

[Maya Erez]

Our experiments showed that the write packing causes degradation of the read 
throughput, in parallel read and write operations.
Since the read latency is critical for user experience we added a write packing control 
mechanism that disables the write packing in case of read requests.
This 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.
The trigger for disabling the write packing is a fetch of a read request.

this patch is dependant in the following patches:
  [PATCH v6 1/3] mmc: core: Add packed command feature of eMMC4.5
  [PATCH v6 2/3] mmc: core: Support packed write command for eMMC4.5 device

Maya Erez (1):
  mmc: block: Add write packing control

 drivers/mmc/card/block.c |   44 ++++++++++++++++++++++++++++++++++++++
 drivers/mmc/card/queue.c |    2 +
 drivers/mmc/card/queue.h |    2 +
 drivers/mmc/core/host.c  |   52 ++++++++++++++++++++++++++++++++++++++++++++++
 include/linux/mmc/host.h |    5 +++-
 5 files changed, 104 insertions(+), 1 deletions(-)

-- 
1.7.3.3
-- 
Sent by a consultant of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.

[PATCH v1 1/1] mmc: block: Add write packing control

[Maya Erez]

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.
The trigger for disabling the write packing is a fetch of a read request.

Signed-off-by: Maya Erez <merez@codeaurora.org>
---
 drivers/mmc/card/block.c |   44 ++++++++++++++++++++++++++++++++++++++
 drivers/mmc/card/queue.c |    2 +
 drivers/mmc/card/queue.h |    2 +
 drivers/mmc/core/host.c  |   52 ++++++++++++++++++++++++++++++++++++++++++++++
 include/linux/mmc/host.h |    5 +++-
 5 files changed, 104 insertions(+), 1 deletions(-)

diff --git a/drivers/mmc/card/block.c b/drivers/mmc/card/block.c
index 2785fd4..c4f7573 100644
--- a/drivers/mmc/card/block.c
+++ b/drivers/mmc/card/block.c
@@ -1313,6 +1313,43 @@ static void mmc_blk_rw_rq_prep(struct mmc_queue_req *mqrq,
 	mmc_queue_bounce_pre(mqrq);
 }
 
+static void mmc_blk_write_packing_control(struct mmc_queue *mq,
+					  struct request *req)
+{
+	struct mmc_host *host = mq->card->host;
+	int data_dir = 0;
+
+	if (!(host->caps2 & MMC_CAP2_PACKED_WR))
+		return;
+
+	if (!(host->caps2 & MMC_CAP2_PACKED_WR_CONTROL)) {
+		mq->write_packing_enabled = 1;
+		return;
+	}
+
+	if (!req || (req && (req->cmd_flags & REQ_FLUSH))) {
+		if (mq->num_of_potential_packed_wr_reqs >
+				host->num_wr_reqs_to_start_packing)
+			mq->write_packing_enabled = 1;
+		return;
+	}
+
+	data_dir = rq_data_dir(req);
+
+	if (data_dir == READ) {
+		mq->num_of_potential_packed_wr_reqs = 0;
+		mq->write_packing_enabled = 0;
+		return;
+	} else if (data_dir == WRITE) {
+		mq->num_of_potential_packed_wr_reqs++;
+	}
+
+	if (mq->num_of_potential_packed_wr_reqs >
+			host->num_wr_reqs_to_start_packing)
+		mq->write_packing_enabled = 1;
+
+}
+
 static u8 mmc_blk_prep_packed_list(struct mmc_queue *mq, struct request *req)
 {
 	struct request_queue *q = mq->queue;
@@ -1332,6 +1369,9 @@ static u8 mmc_blk_prep_packed_list(struct mmc_queue *mq, struct request *req)
 			!card->ext_csd.packed_event_en)
 		goto no_packed;
 
+	if (!mq->write_packing_enabled)
+		goto no_packed;
+
 	if ((rq_data_dir(cur) == WRITE) &&
 			(card->host->caps2 & MMC_CAP2_PACKED_WR))
 		max_packed_rw = card->ext_csd.max_packed_writes;
@@ -1396,6 +1436,8 @@ static u8 mmc_blk_prep_packed_list(struct mmc_queue *mq, struct request *req)
 			break;
 		}
 
+		if (rq_data_dir(next) == WRITE)
+			mq->num_of_potential_packed_wr_reqs++;
 		list_add_tail(&next->queuelist, &mq->mqrq_cur->packed_list);
 		cur = next;
 		reqs++;
@@ -1780,6 +1822,8 @@ static int mmc_blk_issue_rq(struct mmc_queue *mq, struct request *req)
 		goto out;
 	}
 
+	mmc_blk_write_packing_control(mq, req);
+
 	if (req && req->cmd_flags & REQ_DISCARD) {
 		/* complete ongoing async transfer before issuing discard */
 		if (card->host->areq)
diff --git a/drivers/mmc/card/queue.c b/drivers/mmc/card/queue.c
index 165d85a..2d8dcd9 100644
--- a/drivers/mmc/card/queue.c
+++ b/drivers/mmc/card/queue.c
@@ -181,6 +181,8 @@ int mmc_init_queue(struct mmc_queue *mq, struct mmc_card *card,
 	mq->mqrq_cur = mqrq_cur;
 	mq->mqrq_prev = mqrq_prev;
 	mq->queue->queuedata = mq;
+	mq->write_packing_enabled = 0;
+	mq->num_of_potential_packed_wr_reqs = 0;
 
 	blk_queue_prep_rq(mq->queue, mmc_prep_request);
 	queue_flag_set_unlocked(QUEUE_FLAG_NONROT, mq->queue);
diff --git a/drivers/mmc/card/queue.h b/drivers/mmc/card/queue.h
index d761bf1..c5fd2ac 100644
--- a/drivers/mmc/card/queue.h
+++ b/drivers/mmc/card/queue.h
@@ -44,6 +44,8 @@ struct mmc_queue {
 	struct mmc_queue_req	mqrq[2];
 	struct mmc_queue_req	*mqrq_cur;
 	struct mmc_queue_req	*mqrq_prev;
+	int			write_packing_enabled;
+	int			num_of_potential_packed_wr_reqs;
 };
 
 extern int mmc_init_queue(struct mmc_queue *, struct mmc_card *, spinlock_t *,
diff --git a/drivers/mmc/core/host.c b/drivers/mmc/core/host.c
index 91c84c7..9cf1847 100644
--- a/drivers/mmc/core/host.c
+++ b/drivers/mmc/core/host.c
@@ -345,6 +345,8 @@ struct mmc_host *mmc_alloc_host(int extra, struct device *dev)
 	host->max_blk_size = 512;
 	host->max_blk_count = PAGE_CACHE_SIZE / 512;
 
+	host->num_wr_reqs_to_start_packing = 17;
+
 	return host;
 
 free:
@@ -353,6 +355,49 @@ free:
 }
 
 EXPORT_SYMBOL(mmc_alloc_host);
+static ssize_t
+show_num_wr_reqs_to_start_packing(struct device *dev,
+				  struct device_attribute *attr, char *buf)
+{
+	struct mmc_host *host = dev_get_drvdata(dev);
+	int num_wr_reqs_to_start_packing = 0;
+
+	spin_lock(&host->lock);
+	num_wr_reqs_to_start_packing = host->num_wr_reqs_to_start_packing;
+	spin_unlock(&host->lock);
+
+	return snprintf(buf, PAGE_SIZE, "num_wr_reqs_to_start_packing = %d\n",
+					num_wr_reqs_to_start_packing);
+}
+
+static ssize_t
+set_num_wr_reqs_to_start_packing(struct device *dev,
+				 struct device_attribute *attr,
+				 const char *buf, size_t count)
+{
+	int value;
+	struct mmc_host *host = dev_get_drvdata(dev);
+	sscanf(buf, "%d", &value);
+	if (value) {
+		spin_lock(&host->lock);
+		host->num_wr_reqs_to_start_packing = value;
+		spin_unlock(&host->lock);
+	}
+
+	return count;
+}
+
+static DEVICE_ATTR(num_wr_reqs_to_start_packing, S_IRUGO | S_IWUSR,
+		show_num_wr_reqs_to_start_packing,
+		set_num_wr_reqs_to_start_packing);
+
+static struct attribute *dev_attrs[] = {
+	&dev_attr_num_wr_reqs_to_start_packing.attr,
+	NULL,
+};
+static struct attribute_group dev_attr_grp = {
+	.attrs = dev_attrs,
+};
 
 /**
  *	mmc_add_host - initialise host hardware
@@ -380,6 +425,11 @@ int mmc_add_host(struct mmc_host *host)
 #endif
 	mmc_host_clk_sysfs_init(host);
 
+	err = sysfs_create_group(&host->parent->kobj, &dev_attr_grp);
+	if (err)
+		pr_err("%s: failed to create sysfs group with err %d\n",
+		        __func__, err);
+
 	mmc_start_host(host);
 	register_pm_notifier(&host->pm_notify);
 
@@ -405,6 +455,8 @@ void mmc_remove_host(struct mmc_host *host)
 	mmc_remove_host_debugfs(host);
 #endif
 
+	sysfs_remove_group(&host->parent->kobj, &dev_attr_grp);
+
 	device_del(&host->class_dev);
 
 	led_trigger_unregister_simple(host->led);
diff --git a/include/linux/mmc/host.h b/include/linux/mmc/host.h
index 9d0d946..55667a0 100644
--- a/include/linux/mmc/host.h
+++ b/include/linux/mmc/host.h
@@ -242,7 +242,7 @@ struct mmc_host {
 #define MMC_CAP2_PACKED_WR	(1 << 11)	/* Allow packed write */
 #define MMC_CAP2_PACKED_CMD	(MMC_CAP2_PACKED_RD | \
 				 MMC_CAP2_PACKED_WR) /* Allow packed commands */
-
+#define MMC_CAP2_PACKED_WR_CONTROL (1 << 12) /* Allow write packing control */
 	mmc_pm_flag_t		pm_caps;	/* supported pm features */
 	unsigned int        power_notify_type;
 #define MMC_HOST_PW_NOTIFY_NONE		0
@@ -324,6 +324,9 @@ struct mmc_host {
 
 	unsigned int		actual_clock;	/* Actual HC clock rate */
 
+	/* Write packing control attributes */
+	int			num_wr_reqs_to_start_packing;
+
 	unsigned long		private[0] ____cacheline_aligned;
 };
 
-- 
1.7.3.3
-- 
Sent by a consultant of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.