Android: MMC/UFS IO Latency Histograms.

This patch adds a new sysfs node (latency_hist) and reports
IO (svc time) latency histograms. Disabled by default, can be
enabled by echoing 0 into latency_hist, stats can be cleared
by writing 2 into latency_hist.

Bug: 30677035
Change-Id: I0ef42521ff7c44bc08b649183e3b250ac726b318
Signed-off-by: Mohan Srinivasan <srmohan@google.com>

9 files changed, 320 insertions, 3 deletions

diff --git a/block/blk-core.c b/block/blk-core.c
index 03b5f8d77f37..a06394fcbdf5 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -3364,3 +3364,83 @@ int __init blk_dev_init(void)
 
 	return 0;
 }
+
+/*
+ * Blk IO latency support. We want this to be as cheap as possible, so doing
+ * this lockless (and avoiding atomics), a few off by a few errors in this
+ * code is not harmful, and we don't want to do anything that is
+ * perf-impactful.
+ * TODO : If necessary, we can make the histograms per-cpu and aggregate
+ * them when printing them out.
+ */
+void
+blk_zero_latency_hist(struct io_latency_state *s)
+{
+	memset(s->latency_y_axis_read, 0,
+	       sizeof(s->latency_y_axis_read));
+	memset(s->latency_y_axis_write, 0,
+	       sizeof(s->latency_y_axis_write));
+	s->latency_reads_elems = 0;
+	s->latency_writes_elems = 0;
+}
+
+ssize_t
+blk_latency_hist_show(struct io_latency_state *s, char *buf)
+{
+	int i;
+	int bytes_written = 0;
+	int pct, num_elem;
+	u_int64_t elem;
+
+	num_elem = s->latency_reads_elems;
+	if (num_elem > 0) {
+		bytes_written += scnprintf(buf + bytes_written,
+			   PAGE_SIZE - bytes_written,
+			   "IO svc_time Read Latency Histogram (n = %d):\n",
+			   num_elem);
+		for (i = 0;
+		     i < ARRAY_SIZE(latency_x_axis_us);
+		     i++) {
+			elem = s->latency_y_axis_read[i];
+			pct = (elem * 100) / num_elem;
+			bytes_written += scnprintf(buf + bytes_written,
+						   PAGE_SIZE - bytes_written,
+						   "\t< %5lluus%15llu%15d%%\n",
+						   latency_x_axis_us[i],
+						   elem, pct);
+		}
+		/* Last element in y-axis table is overflow */
+		elem = s->latency_y_axis_read[i];
+		pct = (elem * 100) / num_elem;
+		bytes_written += scnprintf(buf + bytes_written,
+					   PAGE_SIZE - bytes_written,
+					   "\t> %5dms%15llu%15d%%\n", 10,
+					   elem, pct);
+	}
+	num_elem = s->latency_writes_elems;
+	if (num_elem > 0) {
+		bytes_written += scnprintf(buf + bytes_written,
+			   PAGE_SIZE - bytes_written,
+			   "IO svc_time Write Latency Histogram (n = %d):\n",
+			   num_elem);
+		for (i = 0;
+		     i < ARRAY_SIZE(latency_x_axis_us);
+		     i++) {
+			elem = s->latency_y_axis_write[i];
+			pct = (elem * 100) / num_elem;
+			bytes_written += scnprintf(buf + bytes_written,
+						   PAGE_SIZE - bytes_written,
+						   "\t< %5lluus%15llu%15d%%\n",
+						   latency_x_axis_us[i],
+						   elem, pct);
+		}
+		/* Last element in y-axis table is overflow */
+		elem = s->latency_y_axis_write[i];
+		pct = (elem * 100) / num_elem;
+		bytes_written += scnprintf(buf + bytes_written,
+					   PAGE_SIZE - bytes_written,
+					   "\t> %5dms%15llu%15d%%\n", 10,
+					   elem, pct);
+	}
+	return bytes_written;
+}
diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
index ebfb3606f7a3..f0cb3ad3421f 100644
--- a/drivers/mmc/core/core.c
+++ b/drivers/mmc/core/core.c
@@ -169,6 +169,17 @@ void mmc_request_done(struct mmc_host *host, struct mmc_request *mrq)
 			pr_debug("%s:     %d bytes transferred: %d\n",
 				mmc_hostname(host),
 				mrq->data->bytes_xfered, mrq->data->error);
+			if (mrq->lat_hist_enabled) {
+				ktime_t completion;
+				u_int64_t delta_us;
+
+				completion = ktime_get();
+				delta_us = ktime_us_delta(completion,
+							  mrq->io_start);
+				blk_update_latency_hist(&host->io_lat_s,
+					(mrq->data->flags & MMC_DATA_READ),
+					delta_us);
+			}
 			trace_mmc_blk_rw_end(cmd->opcode, cmd->arg, mrq->data);
 		}
 
@@ -577,6 +588,11 @@ struct mmc_async_req *mmc_start_req(struct mmc_host *host,
 	}
 
 	if (!err && areq) {
+		if (host->latency_hist_enabled) {
+			areq->mrq->io_start = ktime_get();
+			areq->mrq->lat_hist_enabled = 1;
+		} else
+			areq->mrq->lat_hist_enabled = 0;
 		trace_mmc_blk_rw_start(areq->mrq->cmd->opcode,
 				       areq->mrq->cmd->arg,
 				       areq->mrq->data);
@@ -1871,7 +1887,7 @@ void mmc_init_erase(struct mmc_card *card)
 }
 
 static unsigned int mmc_mmc_erase_timeout(struct mmc_card *card,
-				          unsigned int arg, unsigned int qty)
+					  unsigned int arg, unsigned int qty)
 {
 	unsigned int erase_timeout;
 
@@ -2777,6 +2793,54 @@ static void __exit mmc_exit(void)
 	destroy_workqueue(workqueue);
 }
 
+static ssize_t
+latency_hist_show(struct device *dev, struct device_attribute *attr, char *buf)
+{
+	struct mmc_host *host = cls_dev_to_mmc_host(dev);
+
+	return blk_latency_hist_show(&host->io_lat_s, buf);
+}
+
+/*
+ * Values permitted 0, 1, 2.
+ * 0 -> Disable IO latency histograms (default)
+ * 1 -> Enable IO latency histograms
+ * 2 -> Zero out IO latency histograms
+ */
+static ssize_t
+latency_hist_store(struct device *dev, struct device_attribute *attr,
+		   const char *buf, size_t count)
+{
+	struct mmc_host *host = cls_dev_to_mmc_host(dev);
+	long value;
+
+	if (kstrtol(buf, 0, &value))
+		return -EINVAL;
+	if (value == BLK_IO_LAT_HIST_ZERO)
+		blk_zero_latency_hist(&host->io_lat_s);
+	else if (value == BLK_IO_LAT_HIST_ENABLE ||
+		 value == BLK_IO_LAT_HIST_DISABLE)
+		host->latency_hist_enabled = value;
+	return count;
+}
+
+static DEVICE_ATTR(latency_hist, S_IRUGO | S_IWUSR,
+		   latency_hist_show, latency_hist_store);
+
+void
+mmc_latency_hist_sysfs_init(struct mmc_host *host)
+{
+	if (device_create_file(&host->class_dev, &dev_attr_latency_hist))
+		dev_err(&host->class_dev,
+			"Failed to create latency_hist sysfs entry\n");
+}
+
+void
+mmc_latency_hist_sysfs_exit(struct mmc_host *host)
+{
+	device_remove_file(&host->class_dev, &dev_attr_latency_hist);
+}
+
 subsys_initcall(mmc_init);
 module_exit(mmc_exit);
 
diff --git a/drivers/mmc/core/host.c b/drivers/mmc/core/host.c
index a3d94d1675f5..b59b585dbd6c 100644
--- a/drivers/mmc/core/host.c
+++ b/drivers/mmc/core/host.c
@@ -32,8 +32,6 @@
 #include "slot-gpio.h"
 #include "pwrseq.h"
 
-#define cls_dev_to_mmc_host(d)	container_of(d, struct mmc_host, class_dev)
-
 static DEFINE_IDR(mmc_host_idr);
 static DEFINE_SPINLOCK(mmc_host_lock);
 
@@ -547,6 +545,8 @@ int mmc_add_host(struct mmc_host *host)
 #endif
 	mmc_host_clk_sysfs_init(host);
 
+	mmc_latency_hist_sysfs_init(host);
+
 	mmc_start_host(host);
 	if (!(host->pm_flags & MMC_PM_IGNORE_PM_NOTIFY))
 		register_pm_notifier(&host->pm_notify);
@@ -575,6 +575,8 @@ void mmc_remove_host(struct mmc_host *host)
 	mmc_remove_host_debugfs(host);
 #endif
 
+	mmc_latency_hist_sysfs_exit(host);
+
 	device_del(&host->class_dev);
 
 	led_trigger_unregister_simple(host->led);
diff --git a/drivers/mmc/core/host.h b/drivers/mmc/core/host.h
index f2ab9e578126..4dcf49937ecd 100644
--- a/drivers/mmc/core/host.h
+++ b/drivers/mmc/core/host.h
@@ -12,8 +12,13 @@
 #define _MMC_CORE_HOST_H
 #include <linux/mmc/host.h>
 
+#define cls_dev_to_mmc_host(d)	container_of(d, struct mmc_host, class_dev)
+
 int mmc_register_host_class(void);
 void mmc_unregister_host_class(void);
 
+void mmc_latency_hist_sysfs_init(struct mmc_host *host);
+void mmc_latency_hist_sysfs_exit(struct mmc_host *host);
+
 #endif
 
diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c
index 648a44675880..2188c0af45c1 100644
--- a/drivers/scsi/ufs/ufshcd.c
+++ b/drivers/scsi/ufs/ufshcd.c
@@ -39,6 +39,7 @@
 
 #include <linux/async.h>
 #include <linux/devfreq.h>
+#include <linux/blkdev.h>
 
 #include "ufshcd.h"
 #include "unipro.h"
@@ -1316,6 +1317,17 @@ static int ufshcd_queuecommand(struct Scsi_Host *host, struct scsi_cmnd *cmd)
 		clear_bit_unlock(tag, &hba->lrb_in_use);
 		goto out;
 	}
+
+	/* IO svc time latency histogram */
+	if (hba != NULL && cmd->request != NULL) {
+		if (hba->latency_hist_enabled &&
+		    (cmd->request->cmd_type == REQ_TYPE_FS)) {
+			cmd->request->lat_hist_io_start = ktime_get();
+			cmd->request->lat_hist_enabled = 1;
+		} else
+			cmd->request->lat_hist_enabled = 0;
+	}
+
 	WARN_ON(hba->clk_gating.state != CLKS_ON);
 
 	lrbp = &hba->lrb[tag];
@@ -3065,6 +3077,7 @@ static void ufshcd_transfer_req_compl(struct ufs_hba *hba)
 	u32 tr_doorbell;
 	int result;
 	int index;
+	struct request *req;
 
 	/* Resetting interrupt aggregation counters first and reading the
 	 * DOOR_BELL afterward allows us to handle all the completed requests.
@@ -3088,6 +3101,22 @@ static void ufshcd_transfer_req_compl(struct ufs_hba *hba)
 			/* Mark completed command as NULL in LRB */
 			lrbp->cmd = NULL;
 			clear_bit_unlock(index, &hba->lrb_in_use);
+			req = cmd->request;
+			if (req) {
+				/* Update IO svc time latency histogram */
+				if (req->lat_hist_enabled) {
+					ktime_t completion;
+					u_int64_t delta_us;
+
+					completion = ktime_get();
+					delta_us = ktime_us_delta(completion,
+						  req->lat_hist_io_start);
+					/* rq_data_dir() => true if WRITE */
+					blk_update_latency_hist(&hba->io_lat_s,
+						(rq_data_dir(req) == READ),
+						delta_us);
+				}
+			}
 			/* Do not touch lrbp after scsi done */
 			cmd->scsi_done(cmd);
 			__ufshcd_release(hba);
@@ -5249,6 +5278,54 @@ out:
 }
 EXPORT_SYMBOL(ufshcd_shutdown);
 
+/*
+ * Values permitted 0, 1, 2.
+ * 0 -> Disable IO latency histograms (default)
+ * 1 -> Enable IO latency histograms
+ * 2 -> Zero out IO latency histograms
+ */
+static ssize_t
+latency_hist_store(struct device *dev, struct device_attribute *attr,
+		   const char *buf, size_t count)
+{
+	struct ufs_hba *hba = dev_get_drvdata(dev);
+	long value;
+
+	if (kstrtol(buf, 0, &value))
+		return -EINVAL;
+	if (value == BLK_IO_LAT_HIST_ZERO)
+		blk_zero_latency_hist(&hba->io_lat_s);
+	else if (value == BLK_IO_LAT_HIST_ENABLE ||
+		 value == BLK_IO_LAT_HIST_DISABLE)
+		hba->latency_hist_enabled = value;
+	return count;
+}
+
+ssize_t
+latency_hist_show(struct device *dev, struct device_attribute *attr,
+		  char *buf)
+{
+	struct ufs_hba *hba = dev_get_drvdata(dev);
+
+	return blk_latency_hist_show(&hba->io_lat_s, buf);
+}
+
+static DEVICE_ATTR(latency_hist, S_IRUGO | S_IWUSR,
+		   latency_hist_show, latency_hist_store);
+
+static void
+ufshcd_init_latency_hist(struct ufs_hba *hba)
+{
+	if (device_create_file(hba->dev, &dev_attr_latency_hist))
+		dev_err(hba->dev, "Failed to create latency_hist sysfs entry\n");
+}
+
+static void
+ufshcd_exit_latency_hist(struct ufs_hba *hba)
+{
+	device_create_file(hba->dev, &dev_attr_latency_hist);
+}
+
 /**
  * ufshcd_remove - de-allocate SCSI host and host memory space
  *		data structure memory
@@ -5264,6 +5341,7 @@ void ufshcd_remove(struct ufs_hba *hba)
 	scsi_host_put(hba->host);
 
 	ufshcd_exit_clk_gating(hba);
+	ufshcd_exit_latency_hist(hba);
 	if (ufshcd_is_clkscaling_enabled(hba))
 		devfreq_remove_device(hba->devfreq);
 	ufshcd_hba_exit(hba);
@@ -5553,6 +5631,8 @@ int ufshcd_init(struct ufs_hba *hba, void __iomem *mmio_base, unsigned int irq)
 	/* Hold auto suspend until async scan completes */
 	pm_runtime_get_sync(dev);
 
+	ufshcd_init_latency_hist(hba);
+
 	/*
 	 * The device-initialize-sequence hasn't been invoked yet.
 	 * Set the device to power-off state
@@ -5567,6 +5647,7 @@ out_remove_scsi_host:
 	scsi_remove_host(hba->host);
 exit_gating:
 	ufshcd_exit_clk_gating(hba);
+	ufshcd_exit_latency_hist(hba);
 out_disable:
 	hba->is_irq_enabled = false;
 	scsi_host_put(host);
diff --git a/drivers/scsi/ufs/ufshcd.h b/drivers/scsi/ufs/ufshcd.h
index b47ff07698e8..85f64502c375 100644
--- a/drivers/scsi/ufs/ufshcd.h
+++ b/drivers/scsi/ufs/ufshcd.h
@@ -482,6 +482,9 @@ struct ufs_hba {
 	struct devfreq *devfreq;
 	struct ufs_clk_scaling clk_scaling;
 	bool is_sys_suspended;
+
+	int			latency_hist_enabled;
+	struct io_latency_state io_lat_s;
 };
 
 /* Returns true if clocks can be gated. Otherwise false */
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 5d93a6645e88..efdf6a6d0b36 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -209,6 +209,9 @@ struct request {
 
 	/* for bidi */
 	struct request *next_rq;
+
+	ktime_t			lat_hist_io_start;
+	int			lat_hist_enabled;
 };
 
 static inline unsigned short req_get_ioprio(struct request *req)
@@ -1623,6 +1626,79 @@ extern int bdev_write_page(struct block_device *, sector_t, struct page *,
 						struct writeback_control *);
 extern long bdev_direct_access(struct block_device *, sector_t, void **addr,
 						unsigned long *pfn, long size);
+
+/*
+ * X-axis for IO latency histogram support.
+ */
+static const u_int64_t latency_x_axis_us[] = {
+	100,
+	200,
+	300,
+	400,
+	500,
+	600,
+	700,
+	800,
+	900,
+	1000,
+	1200,
+	1400,
+	1600,
+	1800,
+	2000,
+	2500,
+	3000,
+	4000,
+	5000,
+	6000,
+	7000,
+	9000,
+	10000
+};
+
+#define BLK_IO_LAT_HIST_DISABLE         0
+#define BLK_IO_LAT_HIST_ENABLE          1
+#define BLK_IO_LAT_HIST_ZERO            2
+
+struct io_latency_state {
+	u_int64_t	latency_y_axis_read[ARRAY_SIZE(latency_x_axis_us) + 1];
+	u_int64_t	latency_reads_elems;
+	u_int64_t	latency_y_axis_write[ARRAY_SIZE(latency_x_axis_us) + 1];
+	u_int64_t	latency_writes_elems;
+};
+
+static inline void
+blk_update_latency_hist(struct io_latency_state *s,
+			int read,
+			u_int64_t delta_us)
+{
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(latency_x_axis_us); i++) {
+		if (delta_us < (u_int64_t)latency_x_axis_us[i]) {
+			if (read)
+				s->latency_y_axis_read[i]++;
+			else
+				s->latency_y_axis_write[i]++;
+			break;
+		}
+	}
+	if (i == ARRAY_SIZE(latency_x_axis_us)) {
+		/* Overflowed the histogram */
+		if (read)
+			s->latency_y_axis_read[i]++;
+		else
+			s->latency_y_axis_write[i]++;
+	}
+	if (read)
+		s->latency_reads_elems++;
+	else
+		s->latency_writes_elems++;
+}
+
+void blk_zero_latency_hist(struct io_latency_state *s);
+ssize_t blk_latency_hist_show(struct io_latency_state *s, char *buf);
+
 #else /* CONFIG_BLOCK */
 
 struct block_device;
diff --git a/include/linux/mmc/core.h b/include/linux/mmc/core.h
index de722d4e9d61..1510a383653d 100644
--- a/include/linux/mmc/core.h
+++ b/include/linux/mmc/core.h
@@ -135,6 +135,8 @@ struct mmc_request {
 	struct completion	completion;
 	void			(*done)(struct mmc_request *);/* completion function */
 	struct mmc_host		*host;
+	ktime_t			io_start;
+	int			lat_hist_enabled;
 };
 
 struct mmc_card;
diff --git a/include/linux/mmc/host.h b/include/linux/mmc/host.h
index a233a53ed4e5..31f22edaa581 100644
--- a/include/linux/mmc/host.h
+++ b/include/linux/mmc/host.h
@@ -15,6 +15,7 @@
 #include <linux/sched.h>
 #include <linux/device.h>
 #include <linux/fault-inject.h>
+#include <linux/blkdev.h>
 
 #include <linux/mmc/core.h>
 #include <linux/mmc/card.h>
@@ -379,6 +380,9 @@ struct mmc_host {
 	} embedded_sdio_data;
 #endif
 
+	int			latency_hist_enabled;
+	struct io_latency_state io_lat_s;
+
 	unsigned long		private[0] ____cacheline_aligned;
 };