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. This commit fixes the 32 bit
build breakage in the previous commit. Tested on both 32 bit
and 64 bit arm devices.

Bug: 30677035
Change-Id: I9a615a16616d80f87e75676ac4d078a5c429dcf9
Signed-off-by: Mohan Srinivasan <srmohan@google.com>

1 files changed, 82 insertions, 0 deletions

diff --git a/block/blk-core.c b/block/blk-core.c
index f8e64cac981a..b20ada4ad68e 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -40,6 +40,8 @@
 #include "blk.h"
 #include "blk-mq.h"
 
+#include <linux/math64.h>
+
 EXPORT_TRACEPOINT_SYMBOL_GPL(block_bio_remap);
 EXPORT_TRACEPOINT_SYMBOL_GPL(block_rq_remap);
 EXPORT_TRACEPOINT_SYMBOL_GPL(block_bio_complete);
@@ -3539,3 +3541,83 @@ 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;
+	u_int64_t num_elem, elem;
+	int pct;
+
+	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 = %llu):\n",
+			   num_elem);
+		for (i = 0;
+		     i < ARRAY_SIZE(latency_x_axis_us);
+		     i++) {
+			elem = s->latency_y_axis_read[i];
+			pct = div64_u64(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 = div64_u64(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 = %llu):\n",
+			   num_elem);
+		for (i = 0;
+		     i < ARRAY_SIZE(latency_x_axis_us);
+		     i++) {
+			elem = s->latency_y_axis_write[i];
+			pct = div64_u64(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 = div64_u64(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;
+}