blkdev: Refactoring block io latency histogram codes

The current io_latency_state structure includes entries for read
and write requests. There are special types of write commands
such as sync and discard (trim) commands, and the current
implementation is not general enough if we want to separate
latency histogram for such special commands.

This change makes io_latency_state structure request-type neutral.
It also changes to print the latency average.

Signed-off-by: Hyojun Kim <hyojun@google.com>

1 files changed, 30 insertions, 63 deletions

diff --git a/block/blk-core.c b/block/blk-core.c
index d1788778dd06..aac018436fb8 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -3574,76 +3574,43 @@ int __init blk_dev_init(void)
  * 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;
-}
-EXPORT_SYMBOL(blk_zero_latency_hist);
-
 ssize_t
-blk_latency_hist_show(struct io_latency_state *s, char *buf)
+blk_latency_hist_show(char* name, struct io_latency_state *s, char *buf,
+		int buf_size)
 {
 	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);
+	u_int64_t average;
+
+       num_elem = s->latency_elems;
+       if (num_elem > 0) {
+	       average = div64_u64(s->latency_sum, s->latency_elems);
+	       bytes_written += scnprintf(buf + bytes_written,
+			       buf_size - bytes_written,
+			       "IO svc_time %s Latency Histogram (n = %llu,"
+			       " average = %llu):\n", name, num_elem, average);
+	       for (i = 0;
+		    i < ARRAY_SIZE(latency_x_axis_us);
+		    i++) {
+		       elem = s->latency_y_axis[i];
+		       pct = div64_u64(elem * 100, num_elem);
+		       bytes_written += scnprintf(buf + bytes_written,
+				       PAGE_SIZE - bytes_written,
+				       "\t< %6lluus%15llu%15d%%\n",
+				       latency_x_axis_us[i],
+				       elem, pct);
+	       }
+	       /* Last element in y-axis table is overflow */
+	       elem = s->latency_y_axis[i];
+	       pct = div64_u64(elem * 100, num_elem);
+	       bytes_written += scnprintf(buf + bytes_written,
+			       PAGE_SIZE - bytes_written,
+			       "\t>=%6lluus%15llu%15d%%\n",
+			       latency_x_axis_us[i - 1], elem, pct);
 	}
+
 	return bytes_written;
 }
 EXPORT_SYMBOL(blk_latency_hist_show);