-----Original Message-----
From: Ilya Maximets <i.maxim...@samsung.com>
Date: Friday, August 11, 2017 at 6:01 AM
To: "ovs-dev@openvswitch.org" <ovs-dev@openvswitch.org>
Cc: Heetae Ahn <heetae82....@samsung.com>, Antonio Fischetti 
<antonio.fische...@intel.com>, Darrell Ball <db...@vmware.com>, Ilya Maximets 
<i.maxim...@samsung.com>, Jan Scheurich <jan.scheur...@ericsson.com>
Subject: [PATCH] dpif-netdev: Fix per packet cycles statistics.

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


It would seem unlikely that the addition of 3 stats numbers, done once in the 
code, could go wrong.

Maybe the root cause here is that we don’t have stats names that makes the 
meaning
clear which is a subcategory of stat; maybe some defined APIs would also help 
here.


    
    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 reflects 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.scheur...@ericsson.com>
    Fixes: 3453b4d62a98 ("dpif-netdev: dpcls per in_port with sorted subtables")
    Signed-off-by: Ilya Maximets <i.maxim...@samsung.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];
    -- 
    2.7.4
    
    

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