This article discusses PFE cores in Branch SRXs.

When running "show system processes extensive" you see at least 1 of these processes:

96249 root 123 0 1961M 1235M CPU1 1 52.1H 93.21% flowd_octeon_hm

96249 root 123 0 1961M 1235M CPU15 f 52.1H 93.21% flowd_octeon_hm

96249 root 123 0 1961M 1235M CPU14 e 52.1H 93.21% flowd_octeon_hm

96249 root 123 0 1961M 1235M CPU13 d 52.1H 93.21% flowd_octeon_hm

96249 root 123 0 1961M 1235M CPU12 c 52.1H 93.21% flowd_octeon_hm

96249 root 123 0 1961M 1235M CPU9 9 52.1H 93.21% flowd_octeon_hm

96249 root 123 0 1961M 1235M CPU8 8 52.1H 93.21% flowd_octeon_hm

96249 root 123 0 1961M 1235M CPU7 7 52.1H 93.21% flowd_octeon_hm

96249 root 123 0 1961M 1235M CPU5 5 52.1H 93.21% flowd_octeon_hm

96249 root 123 0 1961M 1235M CPU3 3 52.1H 93.21% flowd_octeon_hm

96249 root 123 0 1961M 1235M CPU2 2 52.1H 93.21% flowd_octeon_hm

96249 root 123 0 1961M 1235M CPU11 b 52.1H 92.48% flowd_octeon_hm

96249 root 123 0 1961M 1235M CPU6 6 52.1H 92.48% flowd_octeon_hm

96249 root 123 0 1961M 1235M CPU4 4 52.1H 92.48% flowd_octeon_hm

96249 root 123 0 1961M 1235M CPU10 a 52.1H 92.48% flowd_octeon_hm

These are representations of the PFE cores/threads. It is expected that they show high CPU utilization. SRX300 and SRX320 have 1 PFE core, SRX340 and SRX345 have 3 PFE cores, and SRX380 has 15 PFE cores.

For explanation, The SRX uses a multicore processor.  The flowd_octeon thread usually runs at high percentage in order to make sure that all the packets received are processed faster.  This is why flowd reads high always, however it does not mean  the system is busy.