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: I625938135ea33e6e87cf6af1fc7edc136d8b4b32
Signed-off-by: Mohan Srinivasan <srmohan@google.com>

1 files changed, 76 insertions, 0 deletions

diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index c70e3588a48c..faf2c0093527 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -197,6 +197,9 @@ 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)
@@ -1645,6 +1648,79 @@ 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 __pmem **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;