[PATCH v3 1/3] mmc: Add MMC software queue support

[Baolin Wang]

Now the MMC read/write stack will always wait for previous request is
completed by mmc_blk_rw_wait(), before sending a new request to hardware,
or queue a work to complete request, that will bring context switching
overhead, especially for high I/O per second rates, to affect the IO
performance.

Thus this patch introduces MMC software queue interface based on the
hardware command queue engine's interfaces, which is similar with the
hardware command queue engine's idea, that can remove the context
switching. Moreover we set the queue depth as 2 for software queue,
that is enough to let the irq handler always trigger the next request
without a context switch and then ask the blk_mq layer for the next one
to get queued, as well as avoiding a long latency.

>From the fio testing data in cover letter, we can see the software
queue can improve performance obviously with 4K block size, increasing
about 52% for sequential read, increasing about 114% for random read,
increasing about 81% for sequential write, and increasing about 127%
for random write.

Moreover we can expand the software queue interface to support MMC
packed request or packed command in future.

Signed-off-by: Baolin Wang <baolin.wang@xxxxxxxxxx>
---
 drivers/mmc/core/block.c  |   61 ++++++++
 drivers/mmc/core/mmc.c    |   13 +-
 drivers/mmc/core/queue.c  |   25 +++-
 drivers/mmc/host/Kconfig  |    8 ++
 drivers/mmc/host/Makefile |    1 +
 drivers/mmc/host/sqhci.c  |  344 +++++++++++++++++++++++++++++++++++++++++++++
 drivers/mmc/host/sqhci.h  |   53 +++++++
 include/linux/mmc/host.h  |    3 +
 8 files changed, 498 insertions(+), 10 deletions(-)
 create mode 100644 drivers/mmc/host/sqhci.c
 create mode 100644 drivers/mmc/host/sqhci.h

diff --git a/drivers/mmc/core/block.c b/drivers/mmc/core/block.c
index 2c71a43..870462c 100644
--- a/drivers/mmc/core/block.c
+++ b/drivers/mmc/core/block.c
@@ -168,6 +168,11 @@ struct mmc_rpmb_data {
 
 static inline int mmc_blk_part_switch(struct mmc_card *card,
 				      unsigned int part_type);
+static void mmc_blk_rw_rq_prep(struct mmc_queue_req *mqrq,
+			       struct mmc_card *card,
+			       int disable_multi,
+			       struct mmc_queue *mq);
+static void mmc_blk_swq_req_done(struct mmc_request *mrq);
 
 static struct mmc_blk_data *mmc_blk_get(struct gendisk *disk)
 {
@@ -1569,9 +1574,30 @@ static int mmc_blk_cqe_issue_flush(struct mmc_queue *mq, struct request *req)
 	return mmc_blk_cqe_start_req(mq->card->host, mrq);
 }
 
+static int mmc_blk_swq_issue_rw_rq(struct mmc_queue *mq, struct request *req)
+{
+	struct mmc_queue_req *mqrq = req_to_mmc_queue_req(req);
+	struct mmc_host *host = mq->card->host;
+	int err;
+
+	mmc_blk_rw_rq_prep(mqrq, mq->card, 0, mq);
+	mqrq->brq.mrq.done = mmc_blk_swq_req_done;
+	mmc_pre_req(host, &mqrq->brq.mrq);
+
+	err = mmc_cqe_start_req(host, &mqrq->brq.mrq);
+	if (err)
+		mmc_post_req(host, &mqrq->brq.mrq, err);
+
+	return err;
+}
+
 static int mmc_blk_cqe_issue_rw_rq(struct mmc_queue *mq, struct request *req)
 {
 	struct mmc_queue_req *mqrq = req_to_mmc_queue_req(req);
+	struct mmc_host *host = mq->card->host;
+
+	if (host->swq_enabled)
+		return mmc_blk_swq_issue_rw_rq(mq, req);
 
 	mmc_blk_data_prep(mq, mqrq, 0, NULL, NULL);
 
@@ -1957,6 +1983,41 @@ static void mmc_blk_urgent_bkops(struct mmc_queue *mq,
 		mmc_run_bkops(mq->card);
 }
 
+static void mmc_blk_swq_req_done(struct mmc_request *mrq)
+{
+	struct mmc_queue_req *mqrq =
+		container_of(mrq, struct mmc_queue_req, brq.mrq);
+	struct request *req = mmc_queue_req_to_req(mqrq);
+	struct request_queue *q = req->q;
+	struct mmc_queue *mq = q->queuedata;
+	struct mmc_host *host = mq->card->host;
+	unsigned long flags;
+
+	if (mmc_blk_rq_error(&mqrq->brq) ||
+	    mmc_blk_urgent_bkops_needed(mq, mqrq)) {
+		spin_lock_irqsave(&mq->lock, flags);
+		mq->recovery_needed = true;
+		mq->recovery_req = req;
+		spin_unlock_irqrestore(&mq->lock, flags);
+
+		host->cqe_ops->cqe_recovery_start(host);
+
+		schedule_work(&mq->recovery_work);
+		return;
+	}
+
+	mmc_blk_rw_reset_success(mq, req);
+
+	/*
+	 * Block layer timeouts race with completions which means the normal
+	 * completion path cannot be used during recovery.
+	 */
+	if (mq->in_recovery)
+		mmc_blk_cqe_complete_rq(mq, req);
+	else
+		blk_mq_complete_request(req);
+}
+
 void mmc_blk_mq_complete(struct request *req)
 {
 	struct mmc_queue *mq = req->q->queuedata;
diff --git a/drivers/mmc/core/mmc.c b/drivers/mmc/core/mmc.c
index c880489..8eac1a2 100644
--- a/drivers/mmc/core/mmc.c
+++ b/drivers/mmc/core/mmc.c
@@ -1852,15 +1852,22 @@ static int mmc_init_card(struct mmc_host *host, u32 ocr,
 	 */
 	card->reenable_cmdq = card->ext_csd.cmdq_en;
 
-	if (card->ext_csd.cmdq_en && !host->cqe_enabled) {
+	if (host->cqe_ops && !host->cqe_enabled) {
 		err = host->cqe_ops->cqe_enable(host, card);
 		if (err) {
 			pr_err("%s: Failed to enable CQE, error %d\n",
 				mmc_hostname(host), err);
 		} else {
 			host->cqe_enabled = true;
-			pr_info("%s: Command Queue Engine enabled\n",
-				mmc_hostname(host));
+
+			if (card->ext_csd.cmdq_en) {
+				pr_info("%s: Command Queue Engine enabled\n",
+					mmc_hostname(host));
+			} else {
+				host->swq_enabled = true;
+				pr_info("%s: Software Queue enabled\n",
+					mmc_hostname(host));
+			}
 		}
 	}
 
diff --git a/drivers/mmc/core/queue.c b/drivers/mmc/core/queue.c
index 7102e2e..2c93c29 100644
--- a/drivers/mmc/core/queue.c
+++ b/drivers/mmc/core/queue.c
@@ -60,7 +60,7 @@ enum mmc_issue_type mmc_issue_type(struct mmc_queue *mq, struct request *req)
 {
 	struct mmc_host *host = mq->card->host;
 
-	if (mq->use_cqe)
+	if (mq->use_cqe && !host->swq_enabled)
 		return mmc_cqe_issue_type(host, req);
 
 	if (req_op(req) == REQ_OP_READ || req_op(req) == REQ_OP_WRITE)
@@ -122,12 +122,14 @@ static enum blk_eh_timer_return mmc_mq_timed_out(struct request *req,
 {
 	struct request_queue *q = req->q;
 	struct mmc_queue *mq = q->queuedata;
+	struct mmc_card *card = mq->card;
+	struct mmc_host *host = card->host;
 	unsigned long flags;
 	int ret;
 
 	spin_lock_irqsave(&mq->lock, flags);
 
-	if (mq->recovery_needed || !mq->use_cqe)
+	if (mq->recovery_needed || !mq->use_cqe || host->swq_enabled)
 		ret = BLK_EH_RESET_TIMER;
 	else
 		ret = mmc_cqe_timed_out(req);
@@ -142,12 +144,13 @@ static void mmc_mq_recovery_handler(struct work_struct *work)
 	struct mmc_queue *mq = container_of(work, struct mmc_queue,
 					    recovery_work);
 	struct request_queue *q = mq->queue;
+	struct mmc_host *host = mq->card->host;
 
 	mmc_get_card(mq->card, &mq->ctx);
 
 	mq->in_recovery = true;
 
-	if (mq->use_cqe)
+	if (mq->use_cqe && !host->swq_enabled)
 		mmc_blk_cqe_recovery(mq);
 	else
 		mmc_blk_mq_recovery(mq);
@@ -158,6 +161,9 @@ static void mmc_mq_recovery_handler(struct work_struct *work)
 	mq->recovery_needed = false;
 	spin_unlock_irq(&mq->lock);
 
+	if (host->swq_enabled)
+		host->cqe_ops->cqe_recovery_finish(host);
+
 	mmc_put_card(mq->card, &mq->ctx);
 
 	blk_mq_run_hw_queues(q, true);
@@ -407,11 +413,16 @@ int mmc_init_queue(struct mmc_queue *mq, struct mmc_card *card)
 	 * The queue depth for CQE must match the hardware because the request
 	 * tag is used to index the hardware queue.
 	 */
-	if (mq->use_cqe)
-		mq->tag_set.queue_depth =
-			min_t(int, card->ext_csd.cmdq_depth, host->cqe_qdepth);
-	else
+	if (mq->use_cqe) {
+		if (host->swq_enabled)
+			mq->tag_set.queue_depth = host->cqe_qdepth;
+		else
+			mq->tag_set.queue_depth =
+				min_t(int, card->ext_csd.cmdq_depth, host->cqe_qdepth);
+	} else {
 		mq->tag_set.queue_depth = MMC_QUEUE_DEPTH;
+	}
+
 	mq->tag_set.numa_node = NUMA_NO_NODE;
 	mq->tag_set.flags = BLK_MQ_F_SHOULD_MERGE | BLK_MQ_F_BLOCKING;
 	mq->tag_set.nr_hw_queues = 1;
diff --git a/drivers/mmc/host/Kconfig b/drivers/mmc/host/Kconfig
index 14d89a1..d117f18 100644
--- a/drivers/mmc/host/Kconfig
+++ b/drivers/mmc/host/Kconfig
@@ -923,6 +923,14 @@ config MMC_CQHCI
 
 	  If unsure, say N.
 
+config MMC_SQHCI
+	bool "Software Queue Host Controller Interface support"
+	help
+	  This selects the Software Queue Host Controller Interface (SQHCI)
+	  support.
+
+	  If unsure, say N.
+
 config MMC_TOSHIBA_PCI
 	tristate "Toshiba Type A SD/MMC Card Interface Driver"
 	depends on PCI
diff --git a/drivers/mmc/host/Makefile b/drivers/mmc/host/Makefile
index 7357871..a3588d4 100644
--- a/drivers/mmc/host/Makefile
+++ b/drivers/mmc/host/Makefile
@@ -97,6 +97,7 @@ obj-$(CONFIG_MMC_SDHCI_BRCMSTB)		+= sdhci-brcmstb.o
 obj-$(CONFIG_MMC_SDHCI_OMAP)		+= sdhci-omap.o
 obj-$(CONFIG_MMC_SDHCI_SPRD)		+= sdhci-sprd.o
 obj-$(CONFIG_MMC_CQHCI)			+= cqhci.o
+obj-$(CONFIG_MMC_SQHCI)			+= sqhci.o
 
 ifeq ($(CONFIG_CB710_DEBUG),y)
 	CFLAGS-cb710-mmc	+= -DDEBUG
diff --git a/drivers/mmc/host/sqhci.c b/drivers/mmc/host/sqhci.c
new file mode 100644
index 0000000..c172bc1
--- /dev/null
+++ b/drivers/mmc/host/sqhci.c
@@ -0,0 +1,344 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * MMC software queue support based on command queue interfaces
+ *
+ * Copyright (C) 2019 Linaro, Inc.
+ * Author: Baolin Wang <baolin.wang@xxxxxxxxxx>
+ */
+
+#include <linux/mmc/card.h>
+#include <linux/mmc/host.h>
+
+#include "sqhci.h"
+
+#define SQHCI_NUM_SLOTS		2
+#define SQHCI_INVALID_TAG	SQHCI_NUM_SLOTS
+
+static void sqhci_pump_requests(struct sqhci_host *sq_host)
+{
+	struct mmc_host *mmc = sq_host->mmc;
+	struct sqhci_slot *slot;
+	unsigned long flags;
+
+	spin_lock_irqsave(&sq_host->lock, flags);
+
+	/* Make sure we are not already running a request now */
+	if (sq_host->mrq) {
+		spin_unlock_irqrestore(&sq_host->lock, flags);
+		return;
+	}
+
+	/* Make sure there are remain requests need to pump */
+	if (!sq_host->qcnt || !sq_host->enabled) {
+		spin_unlock_irqrestore(&sq_host->lock, flags);
+		return;
+	}
+
+	slot = &sq_host->slot[sq_host->next_tag];
+	sq_host->mrq = slot->mrq;
+	sq_host->qcnt--;
+
+	spin_unlock_irqrestore(&sq_host->lock, flags);
+
+	mmc->ops->request(mmc, sq_host->mrq);
+}
+
+static void sqhci_update_next_tag(struct sqhci_host *sq_host, int remains)
+{
+	struct sqhci_slot *slot;
+	int tag;
+
+	/*
+	 * If there are no remain requests in software queue, then set a invalid
+	 * tag.
+	 */
+	if (!remains) {
+		sq_host->next_tag = SQHCI_INVALID_TAG;
+		return;
+	}
+
+	/*
+	 * Increasing the next tag and check if the corresponding request is
+	 * available, if yes, then we found a candidate request.
+	 */
+	if (++sq_host->next_tag != SQHCI_INVALID_TAG) {
+		slot = &sq_host->slot[sq_host->next_tag];
+		if (slot->mrq)
+			return;
+	}
+
+	/* Othersie we should iterate all slots to find a available tag. */
+	for (tag = 0; tag < SQHCI_NUM_SLOTS; tag++) {
+		slot = &sq_host->slot[tag];
+		if (slot->mrq)
+			break;
+	}
+
+	if (tag == SQHCI_NUM_SLOTS)
+		tag = SQHCI_INVALID_TAG;
+
+	sq_host->next_tag = tag;
+}
+
+static void sqhci_post_request(struct sqhci_host *sq_host)
+{
+	unsigned long flags;
+	int remains;
+
+	spin_lock_irqsave(&sq_host->lock, flags);
+
+	remains = sq_host->qcnt;
+	sq_host->mrq = NULL;
+
+	/* Update the next available tag to be queued. */
+	sqhci_update_next_tag(sq_host, remains);
+
+	if (sq_host->waiting_for_idle && !remains) {
+		sq_host->waiting_for_idle = false;
+		wake_up(&sq_host->wait_queue);
+	}
+
+	/* Do not pump new request in recovery mode. */
+	if (sq_host->recovery_halt) {
+		spin_unlock_irqrestore(&sq_host->lock, flags);
+		return;
+	}
+
+	spin_unlock_irqrestore(&sq_host->lock, flags);
+
+	 /*
+	  * Try to pump new request to host controller as fast as possible,
+	  * after completing previous request.
+	  */
+	if (remains > 0)
+		sqhci_pump_requests(sq_host);
+}
+
+/**
+ * sqhci_finalize_request - finalize one request if the request is done
+ * @mmc: the host controller
+ * @mrq: the request need to be finalized
+ *
+ * Return true if we finalized the corresponding request in software queue,
+ * otherwise return false.
+ */
+bool sqhci_finalize_request(struct mmc_host *mmc, struct mmc_request *mrq)
+{
+	struct sqhci_host *sq_host = mmc->cqe_private;
+	unsigned long flags;
+
+	spin_lock_irqsave(&sq_host->lock, flags);
+
+	if (!sq_host->enabled || !sq_host->mrq || sq_host->mrq != mrq) {
+		spin_unlock_irqrestore(&sq_host->lock, flags);
+		return false;
+	}
+
+	/*
+	 * Clear current completed slot request to make a room for new request.
+	 */
+	sq_host->slot[sq_host->next_tag].mrq = NULL;
+
+	spin_unlock_irqrestore(&sq_host->lock, flags);
+
+	mmc_cqe_request_done(mmc, sq_host->mrq);
+
+	sqhci_post_request(sq_host);
+
+	return true;
+}
+EXPORT_SYMBOL_GPL(sqhci_finalize_request);
+
+static void sqhci_recovery_start(struct mmc_host *mmc)
+{
+	struct sqhci_host *sq_host = mmc->cqe_private;
+	unsigned long flags;
+
+	spin_lock_irqsave(&sq_host->lock, flags);
+
+	sq_host->recovery_halt = true;
+
+	spin_unlock_irqrestore(&sq_host->lock, flags);
+}
+
+static void sqhci_recovery_finish(struct mmc_host *mmc)
+{
+	struct sqhci_host *sq_host = mmc->cqe_private;
+	int remains;
+
+	spin_lock_irq(&sq_host->lock);
+
+	sq_host->recovery_halt = false;
+	remains = sq_host->qcnt;
+
+	spin_unlock_irq(&sq_host->lock);
+
+	/*
+	 * Try to pump new request if there are request pending in software
+	 * queue after finishing recovery.
+	 */
+	if (remains > 0)
+		sqhci_pump_requests(sq_host);
+}
+
+static int sqhci_request(struct mmc_host *mmc, struct mmc_request *mrq)
+{
+	struct sqhci_host *sq_host = mmc->cqe_private;
+	int tag = mrq->tag;
+
+	spin_lock_irq(&sq_host->lock);
+
+	if (!sq_host->enabled) {
+		spin_unlock_irq(&sq_host->lock);
+		return -ESHUTDOWN;
+	}
+
+	/* Do not queue any new requests in recovery mode. */
+	if (sq_host->recovery_halt) {
+		spin_unlock_irq(&sq_host->lock);
+		return -EBUSY;
+	}
+
+	sq_host->slot[tag].mrq = mrq;
+
+	/*
+	 * Set the next tag as current request tag if no available
+	 * next tag.
+	 */
+	if (sq_host->next_tag == SQHCI_INVALID_TAG)
+		sq_host->next_tag = tag;
+
+	sq_host->qcnt++;
+
+	spin_unlock_irq(&sq_host->lock);
+
+	sqhci_pump_requests(sq_host);
+
+	return 0;
+}
+
+static void sqhci_post_req(struct mmc_host *mmc, struct mmc_request *mrq)
+{
+	if (mmc->ops->post_req)
+		mmc->ops->post_req(mmc, mrq, 0);
+}
+
+static bool sqhci_queue_is_idle(struct sqhci_host *sq_host, int *ret)
+{
+	bool is_idle;
+
+	spin_lock_irq(&sq_host->lock);
+
+	is_idle = (!sq_host->mrq && !sq_host->qcnt) ||
+		sq_host->recovery_halt;
+
+	*ret = sq_host->recovery_halt ? -EBUSY : 0;
+	sq_host->waiting_for_idle = !is_idle;
+
+	spin_unlock_irq(&sq_host->lock);
+
+	return is_idle;
+}
+
+static int sqhci_wait_for_idle(struct mmc_host *mmc)
+{
+	struct sqhci_host *sq_host = mmc->cqe_private;
+	int ret;
+
+	wait_event(sq_host->wait_queue,
+		   sqhci_queue_is_idle(sq_host, &ret));
+
+	return ret;
+}
+
+static void sqhci_disable(struct mmc_host *mmc)
+{
+	struct sqhci_host *sq_host = mmc->cqe_private;
+	u32 timeout = 500;
+	int ret;
+
+	spin_lock_irq(&sq_host->lock);
+
+	if (!sq_host->enabled) {
+		spin_unlock_irq(&sq_host->lock);
+		return;
+	}
+
+	spin_unlock_irq(&sq_host->lock);
+
+	ret = wait_event_timeout(sq_host->wait_queue,
+				 sqhci_queue_is_idle(sq_host, &ret),
+				 msecs_to_jiffies(timeout));
+	if (ret == 0) {
+		pr_warn("could not stop mmc software queue\n");
+		return;
+	}
+
+	spin_lock_irq(&sq_host->lock);
+
+	sq_host->enabled = false;
+
+	spin_unlock_irq(&sq_host->lock);
+}
+
+static int sqhci_enable(struct mmc_host *mmc, struct mmc_card *card)
+{
+	struct sqhci_host *sq_host = mmc->cqe_private;
+
+	spin_lock_irq(&sq_host->lock);
+
+	if (sq_host->enabled) {
+		spin_unlock_irq(&sq_host->lock);
+		return -EBUSY;
+	}
+
+	sq_host->enabled = true;
+
+	spin_unlock_irq(&sq_host->lock);
+
+	return 0;
+}
+
+static const struct mmc_cqe_ops sqhci_ops = {
+	.cqe_enable = sqhci_enable,
+	.cqe_disable = sqhci_disable,
+	.cqe_request = sqhci_request,
+	.cqe_post_req = sqhci_post_req,
+	.cqe_wait_for_idle = sqhci_wait_for_idle,
+	.cqe_recovery_start = sqhci_recovery_start,
+	.cqe_recovery_finish = sqhci_recovery_finish,
+};
+
+int sqhci_init(struct sqhci_host *sq_host, struct mmc_host *mmc)
+{
+	sq_host->num_slots = SQHCI_NUM_SLOTS;
+	sq_host->next_tag = SQHCI_INVALID_TAG;
+	mmc->cqe_qdepth = SQHCI_NUM_SLOTS;
+
+	sq_host->slot = devm_kcalloc(mmc_dev(mmc), sq_host->num_slots,
+				     sizeof(struct sqhci_slot), GFP_KERNEL);
+	if (!sq_host->slot)
+		return -ENOMEM;
+
+	sq_host->mmc = mmc;
+	sq_host->mmc->cqe_private = sq_host;
+	mmc->cqe_ops = &sqhci_ops;
+
+	spin_lock_init(&sq_host->lock);
+	init_waitqueue_head(&sq_host->wait_queue);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(sqhci_init);
+
+void sqhci_suspend(struct mmc_host *mmc)
+{
+	sqhci_disable(mmc);
+}
+EXPORT_SYMBOL_GPL(sqhci_suspend);
+
+int sqhci_resume(struct mmc_host *mmc)
+{
+	return sqhci_enable(mmc, NULL);
+}
+EXPORT_SYMBOL_GPL(sqhci_resume);
diff --git a/drivers/mmc/host/sqhci.h b/drivers/mmc/host/sqhci.h
new file mode 100644
index 0000000..517e0a5
--- /dev/null
+++ b/drivers/mmc/host/sqhci.h
@@ -0,0 +1,53 @@
+// SPDX-License-Identifier: GPL-2.0
+#ifndef LINUX_MMC_SQHCI_H
+#define LINUX_MMC_SQHCI_H
+
+struct sqhci_slot {
+	struct mmc_request *mrq;
+};
+
+struct sqhci_host {
+	struct mmc_host *mmc;
+	struct mmc_request *mrq;
+	wait_queue_head_t wait_queue;
+	struct sqhci_slot *slot;
+	spinlock_t lock;
+
+	int next_tag;
+	int num_slots;
+	int qcnt;
+
+	bool enabled;
+	bool waiting_for_idle;
+	bool recovery_halt;
+};
+
+#ifdef CONFIG_MMC_SQHCI
+int sqhci_init(struct sqhci_host *sq_host, struct mmc_host *mmc);
+void sqhci_suspend(struct mmc_host *mmc);
+int sqhci_resume(struct mmc_host *mmc);
+bool sqhci_finalize_request(struct mmc_host *mmc, struct mmc_request *mrq);
+#else
+static inline int sqhci_init(struct sqhci_host *sq_host, struct mmc_host *mmc)
+{
+	return -EINVAL;
+}
+
+static inline void sqhci_suspend(struct mmc_host *mmc)
+{
+}
+
+static inline int sqhci_resume(struct mmc_host *mmc)
+{
+	return 0;
+}
+
+static inline bool sqhci_finalize_request(struct mmc_host *mmc,
+					  struct mmc_request *mrq)
+{
+	return false;
+}
+
+#endif
+
+#endif
diff --git a/include/linux/mmc/host.h b/include/linux/mmc/host.h
index 4a351cb..706e2bc 100644
--- a/include/linux/mmc/host.h
+++ b/include/linux/mmc/host.h
@@ -459,6 +459,9 @@ struct mmc_host {
 	bool			cqe_enabled;
 	bool			cqe_on;
 
+	/* Software Queue support */
+	bool			swq_enabled;
+
 	unsigned long		private[0] ____cacheline_aligned;
 };
 
-- 
1.7.9.5