This DisplayString reports the cumulative count of bytes encrypted through IPsec ESP by the hardware accelerator, per 'HW accel. encrypted IPsec ESP bytes.' Since ESP is the payload-encrypting IPsec protocol used by nearly all VPN tunnels, this counter is the direct measure of how much VPN traffic is actually being offloaded to hardware rather than processed by the CPU. A value that stays flat at 0 while VPN tunnels are clearly passing traffic would show the accelerator isn't being used at all for encryption.