Gmod server darkrp 15 fps

Hi, i have a big problem on my server, the max fps we can have is only 20 fps (in the spawn and next to the spawn) when we are 40 players.

It’s a netgraph screen : http://prntscr.com/c5jk7u
I have an ovh dedicated server game, this is the configuration :
Intel i7-4790K
4 Cores / 8 Threads
4,0 GHz / 4,4 GHz
32 Go DDR3 1333 MHz
2 x 240 Go SSD
RAID SOFT

We have ~80 addons (workshop + scriptfodder) we don’t have any leaks.
This is my workshop : http://steamcommunity.com/sharedfiles/filedetails/?id=738941742
And this is my folder addon : http://prntscr.com/c5jlgz http://prntscr.com/c5jlj5

My tickrate is : 16

This is my network settings :
// Network Settings
sv_downloadurl “”
sv_loadingurl “”
net_splitpacket_maxrate 300000
sv_maxrate 0
sv_minrate 50000
sv_maxupdaterate 99
sv_maxcmdrate 99
sv_timeout 120
sv_minupdaterate 10
fps_max 0

And this is my network.cfg :
cl_cmdrate 16
cl_updaterate 16
rate 16000

Thank for help ! And sorry for my bad english i’m french

Enable multicore-rendering.

How can i activate multicore rendering ?

[editline]14th August 2016[/editline]

And i have put the PID of the process of my darkrp server on only 1 core because the PID switch core and it make some lags (i use the command taskset -cp) i have 3 server gmod