Re: [PATCH v1] s390x/tcg: MVCL: Exit to main loop if there are pending interrupts

[Richard Henderson]

On 10/1/19 11:16 AM, David Hildenbrand wrote:
> +static inline bool should_interrupt_instruction(CPUState *cs)
> +{
> +    /*
> +     * Something asked us to stop executing chained TBs, e.g.,
> +     * cpu_interrupt() or cpu_exit().
> +     */
> +    if ((int32_t)atomic_read(&cpu_neg(cs)->icount_decr.u32) < 0) {
> +        return true;
> +    }
> +
> +    /* We have a deliverable interrupt pending. */
> +    if ((atomic_read(&cs->interrupt_request) & CPU_INTERRUPT_HARD) &&
> +        s390_cpu_has_int(S390_CPU(cs))) {
> +        return true;
> +    }
> +    return false;
> +}

The first condition should be true whenever the second condition is true.

In particular, tcg_handle_interrupt sets icount_decr.u16.high = -1 for
qemu_cpu_is_self; otherwise, qemu_cpu_kick calls cpu_exit which does the same
thing.

Think of it this way: we only test icount_decr.u32 at the start of each TB, and
that's the only thing we have that brings us back to the main loop for any
other kind of interrupt.


r~