[PATCH v3 1/5] latencystats: replace use of VLA

[Stephen Hemminger]

The temporary array latencystats is not needed if the algorithm
is converted into one pass.

Signed-off-by: Stephen Hemminger <step...@networkplumber.org>
---
 lib/latencystats/rte_latencystats.c | 31 +++++++++++++++--------------
 1 file changed, 16 insertions(+), 15 deletions(-)

diff --git a/lib/latencystats/rte_latencystats.c 
b/lib/latencystats/rte_latencystats.c
index 4ea9b0d75b..9b345bfb33 100644
--- a/lib/latencystats/rte_latencystats.c
+++ b/lib/latencystats/rte_latencystats.c
@@ -157,9 +157,9 @@ calc_latency(uint16_t pid __rte_unused,
                uint16_t nb_pkts,
                void *_ __rte_unused)
 {
-       unsigned int i, cnt = 0;
+       unsigned int i;
        uint64_t now;
-       float latency[nb_pkts];
+       float latency;
        static float prev_latency;
        /*
         * Alpha represents degree of weighting decrease in EWMA,
@@ -169,13 +169,14 @@ calc_latency(uint16_t pid __rte_unused,
        const float alpha = 0.2;
 
        now = rte_rdtsc();
-       for (i = 0; i < nb_pkts; i++) {
-               if (pkts[i]->ol_flags & timestamp_dynflag)
-                       latency[cnt++] = now - *timestamp_dynfield(pkts[i]);
-       }
 
        rte_spinlock_lock(&glob_stats->lock);
-       for (i = 0; i < cnt; i++) {
+       for (i = 0; i < nb_pkts; i++) {
+               if (!(pkts[i]->ol_flags & timestamp_dynflag))
+                       continue;
+
+               latency = now - *timestamp_dynfield(pkts[i]);
+
                /*
                 * The jitter is calculated as statistical mean of interpacket
                 * delay variation. The "jitter estimate" is computed by taking
@@ -187,22 +188,22 @@ calc_latency(uint16_t pid __rte_unused,
                 * Reference: Calculated as per RFC 5481, sec 4.1,
                 * RFC 3393 sec 4.5, RFC 1889 sec.
                 */
-               glob_stats->jitter +=  (fabsf(prev_latency - latency[i])
+               glob_stats->jitter +=  (fabsf(prev_latency - latency)
                                        - glob_stats->jitter)/16;
                if (glob_stats->min_latency == 0)
-                       glob_stats->min_latency = latency[i];
-               else if (latency[i] < glob_stats->min_latency)
-                       glob_stats->min_latency = latency[i];
-               else if (latency[i] > glob_stats->max_latency)
-                       glob_stats->max_latency = latency[i];
+                       glob_stats->min_latency = latency;
+               else if (latency < glob_stats->min_latency)
+                       glob_stats->min_latency = latency;
+               else if (latency > glob_stats->max_latency)
+                       glob_stats->max_latency = latency;
                /*
                 * The average latency is measured using exponential moving
                 * average, i.e. using EWMA
                 * https://en.wikipedia.org/wiki/Moving_average
                 */
                glob_stats->avg_latency +=
-                       alpha * (latency[i] - glob_stats->avg_latency);
-               prev_latency = latency[i];
+                       alpha * (latency - glob_stats->avg_latency);
+               prev_latency = latency;
        }
        rte_spinlock_unlock(&glob_stats->lock);
 
-- 
2.43.0