testsuite run the defrag latency test solo

this test is time sensitive and it sometimes fail to pass below the
latency threshold, even on strong machines.

this test was the reson we're running just 2 parallel tests in the
github actions CI, revering this.

.github/workflows/ci.yml

@@ -12,9 +12,9 @@ jobs:
     - name: test
       run: |
         sudo apt-get install tcl8.5
-        ./runtest --clients 2 --verbose
+        ./runtest --verbose
     - name: module api test
-      run: ./runtest-moduleapi --clients 2 --verbose
+      run: ./runtest-moduleapi --verbose
 
   build-ubuntu-old:
     runs-on: ubuntu-16.04

tests/test_helper.tcl

@@ -82,6 +82,7 @@ set ::skiptests {}
 set ::allowtags {}
 set ::only_tests {}
 set ::single_tests {}
+set ::run_solo_tests {}
 set ::skip_till ""
 set ::external 0; # If "1" this means, we are running against external instance
 set ::file ""; # If set, runs only the tests in this comma separated list
@@ -112,6 +113,11 @@ proc execute_tests name {
     send_data_packet $::test_server_fd done "$name"
 }
 
+proc execute_code {name code} {
+    eval $code
+    send_data_packet $::test_server_fd done "$name"
+}
+
 # Setup a list to hold a stack of server configs. When calls to start_server
 # are nested, use "srv 0 pid" to get the pid of the inner server. To access
 # outer servers, use "srv -1 pid" etcetera.
@@ -188,6 +194,18 @@ proc s {args} {
     status [srv $level "client"] [lindex $args 0]
 }
 
+# Test wrapped into run_solo are sent back from the client to the
+# test server, so that the test server will send them again to
+# clients once the clients are idle.
+proc run_solo {name code} {
+    if {$::numclients == 1 || $::loop || $::external} {
+        # run_solo is not supported in these scenarios, just run the code.
+        eval $code
+        return
+    }
+    send_data_packet $::test_server_fd run_solo [list $name $code]
+}
+
 proc cleanup {} {
     if {$::dont_clean} {
         return
@@ -337,6 +355,8 @@ proc read_from_test_client fd {
     } elseif {$status eq {server-killed}} {
         set ::active_servers [lsearch -all -inline -not -exact $::active_servers $data]
         set ::active_clients_task($fd) "(KILLED SERVER) pid:$data"
+    } elseif {$status eq {run_solo}} {
+        lappend ::run_solo_tests $data
     } else {
         if {!$::quiet} {
             puts "\[$status\]: $data"
@@ -369,6 +389,13 @@ proc force_kill_all_servers {} {
     }
 }
 
+proc lpop {listVar {count 1}} {
+    upvar 1 $listVar l
+    set ele [lindex $l 0]
+    set l [lrange $l 1 end]
+    set ele
+}
+
 # A new client is idle. Remove it from the list of active clients and
 # if there are still test units to run, launch them.
 proc signal_idle_client fd {
@@ -389,6 +416,14 @@ proc signal_idle_client fd {
         if {$::loop && $::next_test == [llength $::all_tests]} {
             set ::next_test 0
         }
+    } elseif {[llength $::run_solo_tests] != 0 && [llength $::active_clients] == 0} {
+        if {!$::quiet} {
+            puts [colorstr bold-white "Testing solo test"]
+            set ::active_clients_task($fd) "ASSIGNED: $fd solo test"
+        }
+        set ::clients_start_time($fd) [clock seconds]
+        send_data_packet $fd run_code [lpop ::run_solo_tests]
+        lappend ::active_clients $fd
     } else {
         lappend ::idle_clients $fd
         set ::active_clients_task($fd) "SLEEPING, no more units to assign"
@@ -433,6 +468,9 @@ proc test_client_main server_port {
         foreach {cmd data} $payload break
         if {$cmd eq {run}} {
             execute_tests $data
+        } elseif {$cmd eq {run_code}} {
+            foreach {name code} $data break
+            execute_code $name $code
         } else {
             error "Unknown test client command: $cmd"
         }

tests/unit/memefficiency.tcl

@@ -36,6 +36,7 @@ start_server {tags {"memefficiency"}} {
     }
 }
 
+run_solo {defrag} {
 start_server {tags {"defrag"}} {
     if {[string match {*jemalloc*} [s mem_allocator]]} {
         test "Active defrag" {
@@ -328,3 +329,4 @@ start_server {tags {"defrag"}} {
         } {1}
     }
 }
+} ;# run_solo