Re: [Qemu-devel] [PATCH v2 22/45] cpu-exec: lookup/generate TB outside exclusive region during step_atomic

[Richard Henderson]

On 07/16/2017 10:04 AM, Emilio G. Cota wrote:
> Now that all code generation has been converted to check CF_PARALLEL, we can
> generate !CF_PARALLEL code without having yet set !parallel_cpus --
> and therefore without having to be in the exclusive region during
> cpu_exec_step_atomic.
>
> While at it, merge cpu_exec_step into cpu_exec_step_atomic.
>
> Signed-off-by: Emilio G. Cota <address@hidden>
> ---
>   accel/tcg/cpu-exec.c | 26 ++++++++++++--------------
>   1 file changed, 12 insertions(+), 14 deletions(-)
>
> diff --git a/accel/tcg/cpu-exec.c b/accel/tcg/cpu-exec.c
> index efe5c85..23e6d2c 100644
> --- a/accel/tcg/cpu-exec.c
> +++ b/accel/tcg/cpu-exec.c
> @@ -226,7 +226,7 @@ static void cpu_exec_nocache(CPUState *cpu, int max_cycles,
>   }
>   #endif
>   
> -static void cpu_exec_step(CPUState *cpu)
> +void cpu_exec_step_atomic(CPUState *cpu)
>   {
>       CPUClass *cc = CPU_GET_CLASS(cpu);
>       TranslationBlock *tb;
> @@ -239,16 +239,26 @@ static void cpu_exec_step(CPUState *cpu)
>           if (tb == NULL) {
>               mmap_lock();
>               tb_lock();
> -            tb = tb_gen_code(cpu, pc, cs_base, flags, cflags);
> +            tb = tb_htable_lookup(cpu, pc, cs_base, flags, mask_cf(cflags));
> +            if (likely(tb == NULL)) {
> +                tb = tb_gen_code(cpu, pc, cs_base, flags, cflags);
> +            }
>               tb_unlock();
>               mmap_unlock();
>           }
>   
> +        start_exclusive();
> +
> +        /* Since we got here, we know that parallel_cpus must be true.  */
> +        parallel_cpus = false;

Well, since we've moved parallel_cpus completely out of target/*, we no longer 
have to set this false, right?

I wonder how hard it would be to completely hide this variable now...
That said, even that would probably be better as a follow-on cleanup.

Reviewed-by: Richard Henderson <address@hidden>


r~