opcache.jit is on and your web request is unchanged

The JIT compiles hot code paths to machine code and helps almost nothing in a typical web request, where the time is in I/O.

opcache.jit_buffer_size=64M
opcache.jit=tracing

; measured, on a real application:
;   a checkout request:      -1% to +2%
;   a Mandelbrot benchmark:  -70%
;
; the request spends its time in the database, in Redis
; and in serialisation. none of that is JIT-able.

Reporting a benchmark improvement as an application improvement is the mistake this exists to prevent, and it happened widely when 8.0 shipped. Where it genuinely helps is a long-running CPU-bound process — image processing, a large export, a numerical job — which is a small and identifiable set of workloads worth enabling it for specifically.