[ovs-dev] [patch_v5 1/3] dpif-netdev: Fix per packet cycles statistics.

[Darrell Ball]

From: Ilya Maximets <i.maximets at samsung.com>

DP_STAT_LOOKUP_HIT statistics used mistakenly for calculation
of total number of packets. This leads to completely wrong
per packet cycles statistics.

For example:

	emc hits:0
	megaflow hits:253702308
	avg. subtable lookups per hit:1.50
	miss:0
	lost:0
	avg cycles per packet: 248.32 (157498766585/634255770)

	In this case 634255770 total_packets value used for avg
	per packet calculation:

	  total_packets = 'megaflow hits' + 'megaflow hits' * 1.5

	The real value should be 524.38 (157498766585/253702308)

Fix that by summing only stats that reflect match/not match.
It's decided to make direct summing of required values instead of
disabling some stats in a loop to make calculations more clear and
avoid similar issues in the future.

CC: Jan Scheurich <jan.scheurich at ericsson.com>
Fixes: 3453b4d62a98 ("dpif-netdev: dpcls per in_port with sorted subtables")
Signed-off-by: Ilya Maximets <i.maximets at samsung.com>
Acked-by: Jan Scheurich <jan.scheurich at ericsson.com>
---
 lib/dpif-netdev.c | 11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

diff --git a/lib/dpif-netdev.c b/lib/dpif-netdev.c
index e2cd931..17e1666 100644
--- a/lib/dpif-netdev.c
+++ b/lib/dpif-netdev.c
@@ -755,7 +755,7 @@ pmd_info_show_stats(struct ds *reply,
                     unsigned long long stats[DP_N_STATS],
                     uint64_t cycles[PMD_N_CYCLES])
 {
-    unsigned long long total_packets = 0;
+    unsigned long long total_packets;
     uint64_t total_cycles = 0;
     int i;
 
@@ -771,13 +771,12 @@ pmd_info_show_stats(struct ds *reply,
         } else {
             stats[i] = 0;
         }
-
-        if (i != DP_STAT_LOST) {
-            /* Lost packets are already included in DP_STAT_MISS */
-            total_packets += stats[i];
-        }
     }
 
+    /* Sum of all the matched and not matched packets gives the total.  */
+    total_packets = stats[DP_STAT_EXACT_HIT] + stats[DP_STAT_MASKED_HIT]
+                    + stats[DP_STAT_MISS];
+
     for (i = 0; i < PMD_N_CYCLES; i++) {
         if (cycles[i] > pmd->cycles_zero[i]) {
            cycles[i] -= pmd->cycles_zero[i];
-- 
1.9.1