maxplayers launch / command-line parameter has been deprecated. The
maxplayers variable should now be set in
gamemodes_server.txt.example (which should then be renamed to
gamemodes_server.txt), or through the
-maxplayers_override launch/command-line parameter, instead.
This file must be created or otherwise generated from
gamemodes_server.txt.example under the
\csgo\ folder. This
file allows the server administrator to customize each game mode for
their own server. It overrides and defaults set by Valve in
gamemodes.txt. With this file, for example, you can change the
maxrounds for a game type from the default, or enable friendly fire
but reduce the amount of damage friendlies deal.
IT IS IMPORTANT TO MAINTAIN THE SAME HIERARCHY AND SYNTAX AS GAMEMODES.TXT!!! Included with your server installation is a gamemodes_server.txt.example file to help you learn the syntax. There is no file specifically named gamemodes_server.txt in the standard server install. You must rename, copy, or make a new file called gamemodes_server.txt to be able to customize your game modes.
Source: "Counter-Strike: Global Offensive Dedicated Servers - Advanced Configuration" article, Valve Developer Community wiki
See the 'Counter-Strike: Global Offensive Dedicated Servers Known Issues - Maxplayers doesn't work/is overridden' article at the Valve Developer Community wiki, for more info.
Also, CS:GO's priority can be elevated through the launch / command-line parameter,
-high, which will make the computer prioritize its CPU resources for CS:GO, improving performance. See the 'Command Line Options - Source Games' article at the Valve Developer Community wiki, for more info.