Re: [Qemu-devel] [PATCH v6 6/6] cpu-exec: Move TB chaining into tb_find_fast()

["Alex Bennée" <alex.bennee@linaro.org>]

Sergey Fedorov <sergey.fedorov@linaro.org> writes:

> From: Sergey Fedorov <serge.fdrv@gmail.com>
>
> Move tb_add_jump() call and surrounding code from cpu_exec() into
> tb_find_fast(). That simplifies cpu_exec() a little by hiding the direct
> chaining optimization details into tb_find_fast(). It also allows to
> move tb_lock()/tb_unlock() pair into tb_find_fast(), putting it closer
> to tb_find_slow() which also manipulates the lock.
>
> Suggested-by: Alex Bennée <alex.bennee@linaro.org>
> Signed-off-by: Sergey Fedorov <serge.fdrv@gmail.com>
> Signed-off-by: Sergey Fedorov <sergey.fedorov@linaro.org>
> ---
>
> Changes in v6:
>  * Fixed rebase conflicts
>
>  cpu-exec.c | 35 +++++++++++++++++++----------------
>  1 file changed, 19 insertions(+), 16 deletions(-)
>
> diff --git a/cpu-exec.c b/cpu-exec.c
> index f49a436e1a5a..5f23c0660d6e 100644
> --- a/cpu-exec.c
> +++ b/cpu-exec.c
> @@ -320,7 +320,9 @@ found:
>      return tb;
>  }
>
> -static inline TranslationBlock *tb_find_fast(CPUState *cpu)
> +static inline TranslationBlock *tb_find_fast(CPUState *cpu,
> +                                             TranslationBlock **last_tb,
> +                                             int tb_exit)
>  {
>      CPUArchState *env = (CPUArchState *)cpu->env_ptr;
>      TranslationBlock *tb;
> @@ -331,11 +333,24 @@ static inline TranslationBlock *tb_find_fast(CPUState *cpu)
>         always be the same before a given translated block
>         is executed. */
>      cpu_get_tb_cpu_state(env, &pc, &cs_base, &flags);
> +    tb_lock();
>      tb = cpu->tb_jmp_cache[tb_jmp_cache_hash_func(pc)];
>      if (unlikely(!tb || tb->pc != pc || tb->cs_base != cs_base ||
>                   tb->flags != flags)) {
>          tb = tb_find_slow(cpu, pc, cs_base, flags);
>      }
> +    if (cpu->tb_flushed) {
> +        /* Ensure that no TB jump will be modified as the
> +         * translation buffer has been flushed.
> +         */
> +        *last_tb = NULL;
> +        cpu->tb_flushed = false;
> +    }
> +    /* See if we can patch the calling TB. */
> +    if (*last_tb && qemu_loglevel_mask(CPU_LOG_TB_NOCHAIN)) {

This should be !qemu_loglevel_mask(CPU_LOG_TB_NOCHAIN)

> +        tb_add_jump(*last_tb, tb_exit, tb);
> +    }
> +    tb_unlock();
>      return tb;
>  }
>
> @@ -441,7 +456,8 @@ int cpu_exec(CPUState *cpu)
>              } else if (replay_has_exception()
>                         && cpu->icount_decr.u16.low + cpu->icount_extra == 0) {
>                  /* try to cause an exception pending in the log */
> -                cpu_exec_nocache(cpu, 1, tb_find_fast(cpu), true);
> +                last_tb = NULL; /* Avoid chaining TBs */
> +                cpu_exec_nocache(cpu, 1, tb_find_fast(cpu, &last_tb, 0), true);
>                  ret = -1;
>                  break;
>  #endif
> @@ -511,20 +527,7 @@ int cpu_exec(CPUState *cpu)
>                      cpu->exception_index = EXCP_INTERRUPT;
>                      cpu_loop_exit(cpu);
>                  }
> -                tb_lock();
> -                tb = tb_find_fast(cpu);
> -                if (cpu->tb_flushed) {
> -                    /* Ensure that no TB jump will be modified as the
> -                     * translation buffer has been flushed.
> -                     */
> -                    last_tb = NULL;
> -                    cpu->tb_flushed = false;
> -                }
> -                /* See if we can patch the calling TB. */
> -                if (last_tb && !qemu_loglevel_mask(CPU_LOG_TB_NOCHAIN)) {
> -                    tb_add_jump(last_tb, tb_exit, tb);
> -                }
> -                tb_unlock();
> +                tb = tb_find_fast(cpu, &last_tb, tb_exit);
>                  if (likely(!cpu->exit_request)) {
>                      uintptr_t ret;
>                      trace_exec_tb(tb, tb->pc);


--
Alex Bennée