Tuesday 2 October 2007

Results of code profiling mod_multicast with Fprof

I previously presented Fprof and multicast_test. Now I'll illustrate some results I obtained with them.

I tried using normal routing, trusted multicast and untrusted multicast. Both single and multiple servers. And a fixed number of 300 destination addresses.

All those experiments generate a lot of information, so I summarize here only the important results. Times are in milliseconds, and measure the full processing time in the system where the experiments were ran.


Normal - Single

Total: 320
build_packet: 30
ejabberd_router: 275

Normal - Multiple

Total: 630
build_packet: 30
ejabberd_router: 593

Trusted - Single

Total: 410
build_packet: 30
ejabberd_router: 266
mod_multicast: 114
string_to_jid already requires: 52

Trusted - Multiple

Total: 2020
build_packet: 30
ejabberd_router: 700
mod_multicast: 1290
add_addresses consumes too much here: 1067

Untrusted - Single

Total: 500
build_packet: 30
ejabberd_router: 270
mod_multicast: 200
string_to_jid requires: 50

Untrusted - Multiple

Total: 2060
build_packet: 30
ejabberd_router: 640
mod_multicast: 1390
add_addresses consumes too much here: 1070


In those examples, using mod_multicast does not reduce the time consumed by ejabberd_router because the multicast packet is mean to be sent to local users, so the routing process is called 300 times always. If the destinations were not local, and some of them were on the same servers, ejabberd_router would be called less frequently and so the usage of mod_multicast would be noticeable in that aspect too.

The Trusted multicast requires only half of the time required by ejabberd_router itself. In the case of Untrusted, the additional checks make mod_multicast as costly as ejabberd_router.

In the case of Trusted multicast, the function in mod_multicast that consumes the more processing time is jlib:string_to_jid. In Untrusted, the most problematic function is add_addresses. Maybe the code of that function can be improved.

Summarizing, I consider that mod_multicast code is fairly efficient when compared to other parts of ejabberd, specially ejabberd_router.

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