Re: [Qemu-devel] [RFC PATCH 3/4] cpu_exec: Add sleeping algorithm

[Paolo Bonzini]

Il 27/05/2014 16:54, Sebastian Tanase ha scritto:
>                              if (insns_left > 0) {
>                                  /* Execute remaining instructions.  */
>                                  cpu_exec_nocache(env, insns_left, tb);
> +                                if (icount_align_option) {
> +                                    instr_exec_time = original_low -
> +                                                      
> cpu->icount_decr.u16.low;
> +                                    instr_exec_time = instr_exec_time <<
> +                                                      icount_time_shift;
> +                                    diff_clk += instr_exec_time;
> +                                    if (diff_clk > VM_CLOCK_ADVANCE) {
> +                                        delay_host();
> +                                    }
> +                                }

Why doesn't it have to update original_low and original_extra, and
why doesn't it have to take into account original_extra (the new
cpu->icount_extra is zero, but what about the old one)?

> +                    case 1:
> +                    case 0:
> +                        if (icount_align_option) {
> +                            instr_exec_time = original_extra -
> +                                              cpu->icount_extra +
> +                                              original_low -
> +                                              cpu->icount_decr.u16.low;
> +                            instr_exec_time = instr_exec_time <<
> +                                              icount_time_shift;

I wonder if tracking cpu->icount_extra + cpu->icount_decr.u16.low 
(instead of the two separately) will lead to nicer code overall.

       int64_t current_icount = cpu->icount_extra + cpu->icount_decr.u16.low;
       diff_clk += (current_icount - old_icount) << icount_time_shift;
       old_icount = current_icount;

Paolo

> +                            diff_clk += instr_exec_time;
> +                            original_extra = cpu->icount_extra;
> +                            original_low = cpu->icount_decr.u16.low;
> +                        }
> +                        break;

This can go in the "default" label.

>                      default: