Add basic eventloop latency measurement. (#11963)

The measured latency(duration) includes the list below, which can be shown by `INFO STATS`.
```
eventloop_cycles  // ever increasing counter
eventloop_duration_sum // cumulative duration of eventloop in microseconds
eventloop_duration_cmd_sum  // cumulative duration of executing commands in microseconds
instantaneous_eventloop_cycles_per_sec  // average eventloop count per second in recent 1.6s
instantaneous_eventloop_duration_usec  // average single eventloop duration in recent 1.6s
```

Also added some experimental metrics, which are shown only when `INFO DEBUG` is called.
This section isn't included in the default INFO, or even in `INFO ALL` and the fields in this section
can change in the future without considering backwards compatibility.
```
eventloop_duration_aof_sum  // cumulative duration of writing AOF
eventloop_duration_cron_sum  // cumulative duration cron jobs (serverCron, beforeSleep excluding IO and AOF)
eventloop_cmd_per_cycle_max  // max number of commands executed in one eventloop
eventloop_duration_max  // max duration of one eventloop
```

All of these are being reset by CONFIG RESETSTAT

1 files changed, 63 insertions, 0 deletions

diff --git a/tests/unit/info.tcl b/tests/unit/info.tcl
index 759e5bc0b..eb5eee4de 100644
--- a/tests/unit/info.tcl
+++ b/tests/unit/info.tcl
@@ -274,5 +274,68 @@ start_server {tags {"info" "external:skip"}} {
             $rd close
         }
 
+        test {stats: eventloop metrics} {
+            set info1 [r info stats]
+            set cycle1 [getInfoProperty $info1 eventloop_cycles]
+            set el_sum1 [getInfoProperty $info1 eventloop_duration_sum]
+            set cmd_sum1 [getInfoProperty $info1 eventloop_duration_cmd_sum]
+            assert_morethan $cycle1 0
+            assert_morethan $el_sum1 0
+            assert_morethan $cmd_sum1 0
+            after 110 ;# default hz is 10, wait for a cron tick. 
+            set info2 [r info stats]
+            set cycle2 [getInfoProperty $info2 eventloop_cycles]
+            set el_sum2 [getInfoProperty $info2 eventloop_duration_sum]
+            set cmd_sum2 [getInfoProperty $info2 eventloop_duration_cmd_sum]
+            assert_morethan $cycle2 $cycle1
+            assert_lessthan $cycle2 [expr $cycle1+10] ;# we expect 2 or 3 cycles here, but allow some tolerance
+            assert_morethan $el_sum2 $el_sum1
+            assert_lessthan $el_sum2 [expr $el_sum1+5000] ;# we expect roughly 100ms here, but allow some tolerance
+            assert_morethan $cmd_sum2 $cmd_sum1
+            assert_lessthan $cmd_sum2 [expr $cmd_sum1+3000] ;# we expect about tens of ms here, but allow some tolerance
+        }
+ 
+        test {stats: instantaneous metrics} {
+            r config resetstat
+            after 1600 ;# hz is 10, wait for 16 cron tick so that sample array is fulfilled
+            set value [s instantaneous_eventloop_cycles_per_sec]
+            assert_morethan $value 0
+            assert_lessthan $value 15 ;# default hz is 10
+            set value [s instantaneous_eventloop_duration_usec]
+            assert_morethan $value 0
+            assert_lessthan $value 1000 ;# default hz is 10, so duration < 1000 / 10, allow some tolerance
+        }
+
+        test {stats: debug metrics} {
+            # make sure debug info is hidden
+            set info [r info]
+            assert_equal [getInfoProperty $info eventloop_duration_aof_sum] {}
+            set info_all [r info all]
+            assert_equal [getInfoProperty $info_all eventloop_duration_aof_sum] {}
+
+            set info1 [r info debug]
+
+            set aof1 [getInfoProperty $info1 eventloop_duration_aof_sum]
+            assert {$aof1 >= 0}
+            set cron1 [getInfoProperty $info1 eventloop_duration_cron_sum]
+            assert {$cron1 > 0}
+            set cycle_max1 [getInfoProperty $info1 eventloop_cmd_per_cycle_max]
+            assert {$cycle_max1 > 0}
+            set duration_max1 [getInfoProperty $info1 eventloop_duration_max]
+            assert {$duration_max1 > 0}
+
+            after 110 ;# hz is 10, wait for a cron tick.
+            set info2 [r info debug]
+
+            set aof2 [getInfoProperty $info2 eventloop_duration_aof_sum]
+            assert {$aof2 >= $aof1} ;# AOF is disabled, we expect $aof2 == $aof1, but allow some tolerance.
+            set cron2 [getInfoProperty $info2 eventloop_duration_cron_sum]
+            assert_morethan $cron2 $cron1
+            set cycle_max2 [getInfoProperty $info2 eventloop_cmd_per_cycle_max]
+            assert {$cycle_max2 >= $cycle_max1}
+            set duration_max2 [getInfoProperty $info2 eventloop_duration_max]
+            assert {$duration_max2 >= $duration_max1}
+        }
+
     }
 }