Revert LATENCY_HDR_SEC_SIGDIGTS to 2. Optimize summarize_current_seco…

…nd by using hdr_value_at_percentiles() instead of N x hdr_value_at_percentile(). (#295)

deps/hdr_histogram/hdr_histogram.c

@@ -643,28 +643,67 @@ int64_t hdr_min(const struct hdr_histogram* h)
     return non_zero_min(h);
 }
 
+static int64_t get_value_from_idx_up_to_count(const struct hdr_histogram* h, int64_t count_at_percentile)
+{
+    int64_t count_to_idx = 0;
+
+    count_at_percentile = 0 < count_at_percentile ? count_at_percentile : 1;
+    for (int32_t idx = 0; idx < h->counts_len; idx++)
+    {
+        count_to_idx += h->counts[idx];
+        if (count_to_idx >= count_at_percentile)
+        {
+            return hdr_value_at_index(h, idx);
+        }
+    }
+
+    return 0;
+}
+
 int64_t hdr_value_at_percentile(const struct hdr_histogram* h, double percentile)
 {
-    struct hdr_iter iter;
-    int64_t total = 0;
     double requested_percentile = percentile < 100.0 ? percentile : 100.0;
     int64_t count_at_percentile =
         (int64_t) (((requested_percentile / 100) * h->total_count) + 0.5);
-    count_at_percentile = count_at_percentile > 1 ? count_at_percentile : 1;
+    int64_t value_from_idx = get_value_from_idx_up_to_count(h, count_at_percentile);
+    if (percentile == 0.0)
+    {
+        return lowest_equivalent_value(h, value_from_idx);
+    }
+    return highest_equivalent_value(h, value_from_idx);
+}
 
-    hdr_iter_init(&iter, h);
+int hdr_value_at_percentiles(const struct hdr_histogram *h, const double *percentiles, int64_t *values, size_t length)
+{
+    if (NULL == percentiles || NULL == values)
+    {
+        return EINVAL;
+    }
 
-    while (hdr_iter_next(&iter))
+    struct hdr_iter iter;
+    const int64_t total_count = h->total_count;
+    // to avoid allocations we use the values array for intermediate computation
+    // i.e. to store the expected cumulative count at each percentile
+    for (size_t i = 0; i < length; i++)
     {
-        total += iter.count;
+        const double requested_percentile = percentiles[i] < 100.0 ? percentiles[i] : 100.0;
+        const int64_t count_at_percentile =
+        (int64_t) (((requested_percentile / 100) * total_count) + 0.5);
+        values[i] = count_at_percentile > 1 ? count_at_percentile : 1;
+    }
 
-        if (total >= count_at_percentile)
+    hdr_iter_init(&iter, h);
+    int64_t total = 0;
+    size_t at_pos = 0;
+    while (hdr_iter_next(&iter) && at_pos < length)
+    {
+        total += iter.count;
+        while (at_pos < length && total >= values[at_pos])
         {
-            int64_t value_from_index = iter.value;
-            return highest_equivalent_value(h, value_from_index);
+            values[at_pos] = highest_equivalent_value(h, iter.value);
+            at_pos++;
         }
     }
-
     return 0;
 }
 

deps/hdr_histogram/hdr_histogram.h

@@ -284,6 +284,18 @@ int64_t hdr_max(const struct hdr_histogram* h);
  */
 int64_t hdr_value_at_percentile(const struct hdr_histogram* h, double percentile);
 
+/**
+ * Get the values at the given percentiles.
+ *
+ * @param h "This" pointer.
+ * @param percentiles The ordered percentiles array to get the values for.
+ * @param length Number of elements in the arrays.
+ * @param values Destination array containing the values at the given percentiles.
+ * The values array should be allocated by the caller.
+ * @return 0 on success, ENOMEM if the provided destination array is null.
+ */
+int hdr_value_at_percentiles(const struct hdr_histogram *h, const double *percentiles, int64_t *values, size_t length);
+
 /**
  * Gets the standard deviation for the values in the histogram.
  *

run_stats.cpp

@@ -117,8 +117,9 @@ run_stats::run_stats(benchmark_config *config) :
 {
     memset(&m_start_time, 0, sizeof(m_start_time));
     memset(&m_end_time, 0, sizeof(m_end_time));
-    quantiles_list = config->print_percentiles.quantile_list;
-
+    std::vector<float> quantiles_list_float = config->print_percentiles.quantile_list;
+    std::sort(quantiles_list_float.begin(), quantiles_list_float.end());
+    quantiles_list = std::vector<double>(quantiles_list_float.begin(), quantiles_list_float.end());
     if (config->arbitrary_commands->is_defined()) {
         setup_arbitrary_commands(config->arbitrary_commands->size());
     }
@@ -882,7 +883,7 @@ void run_stats::summarize(totals& result) const
 void result_print_to_json(json_handler * jsonhandler, const char * type, double ops_sec,
                           double hits, double miss, double moved, double ask, double kbs, double kbs_rx, double kbs_tx,
                           double latency, long m_total_latency, long ops,
-                          std::vector<float> quantile_list, struct hdr_histogram* latency_histogram, 
+                          std::vector<double> quantile_list, struct hdr_histogram* latency_histogram,
                           std::vector<unsigned int> timestamps, 
                           std::vector<one_sec_cmd_stats> timeserie_stats )
 {

run_stats.h

@@ -97,7 +97,7 @@ class run_stats {
     totals m_totals;
 
     std::list<one_second_stats> m_stats;
-    std::vector<float> quantiles_list;
+    std::vector<double> quantiles_list;
 
     // current second stats ( appended to m_stats and reset every second )
     one_second_stats m_cur_stats;

run_stats_types.cpp

@@ -72,11 +72,14 @@ void one_sec_cmd_stats::merge(const one_sec_cmd_stats& other) {
     m_min_latency = other.m_min_latency < m_min_latency ? other.m_min_latency : m_min_latency;
 }
 
-void one_sec_cmd_stats::summarize_quantiles(safe_hdr_histogram histogram, std::vector<float> quantiles) {
-    for (std::size_t i = 0; i < quantiles.size(); i++){
-        const float quantile = quantiles[i];
-        const double value = hdr_value_at_percentile(histogram, quantile)/ (double) LATENCY_HDR_RESULTS_MULTIPLIER;
-        summarized_quantile_values.push_back(value);
+void one_sec_cmd_stats::summarize_quantiles(safe_hdr_histogram histogram, std::vector<double> sorted_quantiles) {
+    std::vector<int64_t> values(sorted_quantiles.size());
+    int result = hdr_value_at_percentiles(histogram, sorted_quantiles.data(), values.data(), sorted_quantiles.size());
+    if (result != 0) {
+        return;
+    }
+    for (std::size_t i = 0; i < sorted_quantiles.size(); i++) {
+        summarized_quantile_values.push_back(values[i] / static_cast<double>(LATENCY_HDR_RESULTS_MULTIPLIER));
     }
 }
 

run_stats_types.h

@@ -24,7 +24,7 @@
 #define LATENCY_HDR_SIGDIGTS 3
 #define LATENCY_HDR_SEC_MIN_VALUE 10
 #define LATENCY_HDR_SEC_MAX_VALUE 600000000 ## LL
-#define LATENCY_HDR_SEC_SIGDIGTS 3
+#define LATENCY_HDR_SEC_SIGDIGTS 2
 #define LATENCY_HDR_RESULTS_MULTIPLIER 1000
 #define LATENCY_HDR_GRANULARITY 10
 
@@ -90,7 +90,14 @@ class one_sec_cmd_stats {
     one_sec_cmd_stats();
     void reset();
     void merge(const one_sec_cmd_stats& other);
-    void summarize_quantiles(safe_hdr_histogram histogram, std::vector<float> quantiles);
+    /**
+     * Summarizes quantiles from the given histogram.
+     *
+     * @param histogram The histogram from which quantile values are extracted.
+     * @param sorted_quantiles A sorted (ascending order) vector of quantiles for which values will be computed.
+     *                         The caller must ensure the vector is sorted from smallest to largest.
+     */
+    void summarize_quantiles(safe_hdr_histogram histogram, std::vector<double> sorted_quantiles);
     void update_op(unsigned int bytes_rx, unsigned int bytes_tx,  unsigned int latency);
     void update_op(unsigned int bytes_rx, unsigned int bytes_tx,  unsigned int latency, unsigned int hits, unsigned int misses);
     void update_moved_op(unsigned int bytes_rx, unsigned int bytes_tx,  unsigned int latency);