histograms: add script for parsing histogram data

Signed-off-by: Piotr Pelplinski <piotr.pelplinski@intel.com>
Change-Id: I2c4df9593fa7c6aa4fe3408f7851e253f59f26eb
Reviewed-on: https://review.gerrithub.io/c/441583
Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>
Chandler-Test-Pool: SPDK Automated Test System <sys_sgsw@intel.com>
Reviewed-by: Jim Harris <james.r.harris@intel.com>
Reviewed-by: Pawel Wodkowski <pawelx.wodkowski@intel.com>
Reviewed-by: Karol Latecki <karol.latecki@intel.com>
Reviewed-by: Darek Stojaczyk <dariusz.stojaczyk@intel.com>

scripts/histogram.py

@@ -0,0 +1,44 @@
+#!/usr/bin/env python3
+
+import sys
+import json
+import base64
+import struct
+
+buf = sys.stdin.readlines()
+json = json.loads(" ".join(buf))
+histogram = base64.b64decode(json["histogram"])
+bucket_shift = json["bucket_shift"]
+tsc_rate = json["tsc_rate"]
+
+print("Latency histogram")
+print("==============================================================================")
+print("       Range in us     Cumulative    IO count")
+
+so_far = 0
+bucket = 0
+total = 1
+
+for i in range(0, 64 - bucket_shift):
+    for j in range(0, (1 << bucket_shift)):
+        index = (((i << bucket_shift) + j) * 8)
+        total += int.from_bytes(histogram[index:index + 8], 'little')
+
+for i in range(0, 64 - bucket_shift):
+    for j in range(0, (1 << bucket_shift)):
+        index = (((i << bucket_shift) + j)*8)
+        count = int.from_bytes(histogram[index:index + 8], 'little')
+        so_far += count
+        last_bucket = bucket
+
+        if i > 0:
+            bucket = (1 << (i + bucket_shift - 1))
+            bucket += ((j+1) << (i - 1))
+        else:
+            bucket = j+1
+
+        start = last_bucket * 1000 * 1000 / tsc_rate
+        end = bucket * 1000 * 1000 / tsc_rate
+        so_far_pct = so_far * 100.0 / total
+        if count > 0:
+            print("%9.3f - %9.3f: %9.4f%%  (%9u)" % (start, end, so_far_pct, count))