I have R493AH with routerOS 5.4
I have 8 PPPoE servers rununing on the router and i have 150 PPPoE users and might be rise to 300+ users.
the cpu usage is 80% to 100% 
i like advice how to lower my cpu usage, or any other solutions might be helpful
thank you
use PC server for PPPoE, core2duo or core2quad with intel ethernet
Single-core Pentium III 1400MHz with rtl8139 ethernet works fine here for ~100 PPPoE connections (and lots of other things), running Debian but with rp-pppoe rebuilt to upgrade 3.8 to 3.10 and enable kernel mode PPPoE (stock package runs user mode only, more CPU load). Not sure which mode (kernel or user) and rp-pppoe version is used in ROS, it would be nice to know. In some situations you just can’t use a PC due to space/power/noise constraints.
Disable conntrack if you don’t need it
Rework your queueing system, if you are using it
rework your firewall rules…
… the usual stuff 