Refactor the calculation to avoid reduntant time conversions

[NelsonVides]

On shaper.erl, the arithmetics are done by converting to and from native-second time units, which shows on the profiling statistics I gathered last time:

for a scenario like "5k users sending a 1-to-1 message per second"

FUNCTION                              CALLS        %      TIME  [uS / CALLS]
--------                              -----  -------      ----  [----------]
erlang:monotonic_time/0                5999     0.01      1022  [      0.17]
erlang:convert_time_unit/3            11998     0.04      8580  [      0.72]

We see that convert_time_unit/3 is called twice as often as monotonic_time/0, which is exactly what shaper:update/2 does.

On fprof, we can see that, of the accumulated 130us that shaper:update/2 takes, 20us of them are spent on erlang:convert_time_unit/3, plus 4us on erlang:monotonic_time/0, while

{[{{ejabberd_receiver,process_data,2},         1409,  130.061,   51.471}],     
 { {shaper,update,2},                          1409,  130.061,   51.471},     %
 [{{erlang,convert_time_unit,3},               2818,   34.792,   20.457},      
  {{lager_config,get,2},                       1409,   15.401,   10.091},      
  {{erlang,whereis,1},                         2818,    9.563,    9.563},      
  {{erlang,max,2},                             2818,    9.154,    9.154},      
  {{erlang,monotonic_time,0},                  1409,    4.882,    4.882},      
  {{erlang,min,2},                             1409,    4.798,    4.798}]}.    

My main idea to optimise this, is this quote from the erlang:monotonic_time/1 docs:

Same as calling erlang:convert_time_unit(erlang:monotonic_time(), native, Unit), however optimized for commonly used Units.

[mongoose-im]

7504.1 / Erlang 22.0 / small_tests / 64fa7e4
Reports root / small

---

7504.2 / Erlang 22.0 / internal_mnesia / 64fa7e4
Reports root/ big
OK: 1274 / Failed: 0 / User-skipped: 138 / Auto-skipped: 0

---

7504.3 / Erlang 22.0 / odbc_mssql_mnesia / 64fa7e4
Reports root/ big
OK: 2493 / Failed: 0 / User-skipped: 199 / Auto-skipped: 0

---

7504.4 / Erlang 22.0 / mysql_redis / 64fa7e4
Reports root/ big
OK: 2488 / Failed: 0 / User-skipped: 204 / Auto-skipped: 0

---

7504.7 / Erlang 22.0 / elasticsearch_and_cassandra_mnesia / 64fa7e4
Reports root/ big
OK: 328 / Failed: 0 / User-skipped: 28 / Auto-skipped: 0

---

7504.6 / Erlang 22.0 / ldap_mnesia / 64fa7e4
Reports root/ big
OK: 1239 / Failed: 0 / User-skipped: 173 / Auto-skipped: 0

---

7504.5 / Erlang 22.0 / riak_mnesia / 64fa7e4
Reports root/ big
OK: 1407 / Failed: 0 / User-skipped: 145 / Auto-skipped: 0

---

7504.9 / Erlang 21.3 / pgsql_mnesia / 64fa7e4
Reports root/ big / small
OK: 2506 / Failed: 0 / User-skipped: 186 / Auto-skipped: 0

[codecov]

Codecov Report

Merging #2545 into master will increase coverage by 0.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #2545      +/-   ##
==========================================
+ Coverage   78.99%   79.01%   +0.01%     
==========================================
  Files         343      343              
  Lines       29494    29491       -3     
==========================================
+ Hits        23298    23301       +3     
+ Misses       6196     6190       -6

Impacted Files	Coverage Δ
src/shaper.erl	100% <100%> (+5.88%)	⬆️
src/ejabberd_receiver.erl	81.5% <100%> (ø)	⬆️
src/elasticsearch/mongoose_elasticsearch.erl	76.92% <0%> (-7.7%)	⬇️
src/mam/mod_mam_rdbms_prefs.erl	92.59% <0%> (-3.71%)	⬇️
src/rdbms/mongoose_rdbms.erl	69.74% <0%> (-2.06%)	⬇️
src/mam/mod_mam_elasticsearch_arch.erl	89.81% <0%> (-1.86%)	⬇️
src/mam/mod_mam_utils.erl	83.49% <0%> (-0.67%)	⬇️
src/ejabberd_c2s.erl	87.36% <0%> (-0.08%)	⬇️
src/mod_muc_log.erl	77.69% <0%> (ø)	⬆️
src/mod_bosh_socket.erl	81.51% <0%> (+0.33%)	⬆️
... and 2 more

---

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[NelsonVides]

https://circleci.com/workflow-run/d8bcfdb0-29a9-49b4-aa41-bb6938ffd058
https://travis-ci.org/esl/MongooseIM/builds/619549950

[michalwski]

Could you squash these 2 commits into one?

[NelsonVides]

Could you squash these 2 commits into one?

Done :)

[mongoose-im]

7510.1 / Erlang 22.0 / small_tests / a90f120
Reports root / small

---

7510.2 / Erlang 22.0 / internal_mnesia / a90f120
Reports root/ big
OK: 1274 / Failed: 0 / User-skipped: 138 / Auto-skipped: 0

---

7510.3 / Erlang 22.0 / odbc_mssql_mnesia / a90f120
Reports root/ big
OK: 2493 / Failed: 0 / User-skipped: 199 / Auto-skipped: 0

---

7510.4 / Erlang 22.0 / mysql_redis / a90f120
Reports root/ big
OK: 2488 / Failed: 0 / User-skipped: 204 / Auto-skipped: 0

---

7510.7 / Erlang 22.0 / elasticsearch_and_cassandra_mnesia / a90f120
Reports root/ big
OK: 328 / Failed: 0 / User-skipped: 28 / Auto-skipped: 0

---

7510.5 / Erlang 22.0 / riak_mnesia / a90f120
Reports root/ big
OK: 1407 / Failed: 0 / User-skipped: 145 / Auto-skipped: 0

---

7510.6 / Erlang 22.0 / ldap_mnesia / a90f120
Reports root/ big
OK: 1239 / Failed: 0 / User-skipped: 173 / Auto-skipped: 0

---

7510.9 / Erlang 21.3 / pgsql_mnesia / a90f120
Reports root/ big / small
OK: 2506 / Failed: 0 / User-skipped: 186 / Auto-skipped: 0

[fenek]

The PR looks fine but we need a separate PR first that would introduce tests that focus on shapers verification.

[mongoose-im]

7885.1 / Erlang 22.0 / small_tests / 4e51e93
Reports root / small

---

7885.2 / Erlang 22.0 / internal_mnesia / 4e51e93
Reports root/ big
OK: 1378 / Failed: 0 / User-skipped: 155 / Auto-skipped: 0

---

7885.4 / Erlang 22.0 / mysql_redis / 4e51e93
Reports root/ big
OK: 2608 / Failed: 0 / User-skipped: 205 / Auto-skipped: 0

---

7885.3 / Erlang 22.0 / odbc_mssql_mnesia / 4e51e93
Reports root/ big
OK: 2613 / Failed: 0 / User-skipped: 200 / Auto-skipped: 0

---

7885.5 / Erlang 22.0 / riak_mnesia / 4e51e93
Reports root/ big
OK: 1511 / Failed: 0 / User-skipped: 162 / Auto-skipped: 0

---

7885.7 / Erlang 22.0 / elasticsearch_and_cassandra_mnesia / 4e51e93
Reports root/ big
OK: 328 / Failed: 0 / User-skipped: 28 / Auto-skipped: 0

---

7885.6 / Erlang 22.0 / ldap_mnesia / 4e51e93
Reports root/ big
OK: 1343 / Failed: 0 / User-skipped: 190 / Auto-skipped: 0

---

7885.9 / Erlang 21.3 / pgsql_mnesia / 4e51e93
Reports root/ big / small
OK: 2626 / Failed: 0 / User-skipped: 187 / Auto-skipped: 0