[qb45]

Maybe

  perf stat -d php ./benchmark.php

would show some difference? It measures some kernel and CPU events like context switches, page faults, L1 and L3 cache misses.

[erichileman]

Unfortunately <not supported>

Performance counter stats for 'php56 index.php':

        394.588620      task-clock (msec)         #    0.983 CPUs utilized
               226      context-switches          #    0.573 K/sec
                 2      cpu-migrations            #    0.005 K/sec
            17,447      page-faults               #    0.044 M/sec
   <not supported>      cycles
   <not supported>      stalled-cycles-frontend
   <not supported>      stalled-cycles-backend
   <not supported>      instructions
   <not supported>      branches
   <not supported>      branch-misses
   <not supported>      L1-dcache-loads
   <not supported>      L1-dcache-load-misses
   <not supported>      LLC-loads
   <not supported>      LLC-load-misses

       0.401580145 seconds time elapsed

Working on finding the event descriptors...