Results of mod_multicast execution time with timer:tc

I previously presented timer:tc and multicast_test. Now I'll illustrate some results I obtained with them.

I ran 6 experiments, using normal routing, trusted multicast and untrusted multicast; both single and multiple servers. Each experiment was ran for several number of destination addresses.

The time is expressed in microseconds (1 second = 1.000.000 microseconds). Note that the time shown here includes not only mod_multicast, but also packet building and ejabberd_router.


Results

Normal - Single

           #     Exec Time   Time per destination
Destinations (microseconds)        (microseconds)
         1           161                 161.00
       101          6074                  60.14
       201         22163                 110.26
       301         40950                 136.05
       401         74586                 186.00
       501        100445                 200.49
       601        107012                 178.06
       701        131163                 187.11
       801        146473                 182.86
       901        153147                 169.97

Normal - Multiple

           #     Exec Time   Time per destination
Destinations (microseconds)        (microseconds)
         1           196                 196.00
       101         11206                 110.95
       201         20918                 104.07
       301         30811                 102.36
       401         43627                 108.80
       501         52742                 105.27
       601         59650                  99.25
       701         75291                 107.41
       801         81077                 101.22
       901         80192                  89.00

Trusted - Single

           #     Exec Time   Time per destination
Destinations (microseconds)        (microseconds)
         1           226                 226.00
       101          8719                  86.33
       201         39938                 198.70
       301         77040                 255.95
       401        101675                 253.55
       501        122156                 243.82
       601        144422                 240.30
       701        158917                 226.70
       801        186553                 232.90
       901        197387                 219.08

Trusted - Multiple

           #     Exec Time   Time per destination
Destinations (microseconds)        (microseconds)
         1           283                 283.00
       101         21751                 215.36
       201         41077                 204.36
       301         66047                 219.43
       401        102542                 255.72
       501        315313                 629.37
       601        140158                 233.21
       701        164836                 235.14
       801        171249                 213.79
       901        189712                 210.56

Untrusted - Single

            #     Exec Time   Time per destination
Destinations (microseconds)        (microseconds)
          1           317                 317.00
        101         25528                 252.75
        201         79402                 395.03
        301        155075                 515.20
        401        284532                 709.56
        501        329484                 657.65
        601        357879                 595.47
        701        388755                 554.57
        801        414622                 517.63
        901        506557                 562.22

Untrusted - Multiple

            #     Exec Time   Time per destination
Destinations (microseconds)        (microseconds)
          1          1121                1121.00
        101        115736                1157.36
        201        331379                1656.89
        301        601325                2004.42
        400       2478072                6195.18
...

Analysis

What does this show? The computation time per destination address remains constant across different packet sizes. The fluctuations are only due to my computer: it was being used for other tasks, not only running those experiments [1].

For example, processing a packet with 300 destination addresses (few rosters and chatrooms have more than this number of items) costs around 77 milliseconds if the source is trusted (a local MUC service or session manager). The same packet costs 155 milliseconds if the source is not trusted and the packet must be carefully inspected.

In the less bright side of the results, the Multiple set of experiments again perform quite badly compared to Single. Note that part of this is due to the function add_addresses, as explained in the Fprof article. Another part of the problem is not in the server, but in the stressing tool: the building function I implemented in multicast_test puts non-existent servernames when it's run with the 'Multiple' option: "5.localhost", "7.localhost"...


Conclusions

As a summary, the results I obtained using timer:tc are compatible with the previous results I obtained with Fprof and Jabsimul. All them indicate that mod_multicast consumes approximately, in average, as much time as the ejabberd routing functions do.

So, using multicast increases the CPU consumption, as was expected. This cost will be acceptable once the benefits of multicasting are taken into account.

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[1] Statistically speaking, it would be preferable to run a batch of experiments and show only the average and confidence interval, but I guess this is not really required for now.