Re: [Qemu-devel] Speed up hack

[Fabrice Bellard <fabrice@bellard.org>]

Can you estimate the speed gains ? I am especially interested by the 
poll() overhead. For the rest, optimizing DMA_run() would be simpler and 
more efficient.

Fabrice.

Vladimir N. Oleynik wrote:
> Hi.
> 
> I generate little speed up hack:
> 
> 1) new TICKS_BEFORE_POLL constant from make cpu loop before
> call poll().
> 2) call DMA_run() if sb16 or floppy present
> 3) also, for extreme overclocker: if change MAX_FD from 2 to 1,
> you can make very little speed up also ;-)
> 
> 
> --- vl.c~       2004-05-17 20:15:26.000000000 +0400
> +++ vl.c        2004-05-17 19:52:44.000000000 +0400
> @@ -1634,6 +1634,8 @@
>      }
>  }
> 
> +#define TICKS_BEFORE_POLL 100
> +
>  int main_loop(void)
>  {
>  #ifndef _WIN32
> @@ -1641,6 +1643,7 @@
>      IOHandlerRecord *ioh, *ioh_next;
>      uint8_t buf[4096];
>      int n, max_size;
> +    int tick_before_poll=TICKS_BEFORE_POLL;
>  #endif
>      int ret, timeout;
>      CPUState *env = global_env;
> @@ -1670,6 +1673,11 @@
>             Sleep(timeout);
>  #else
> 
> +       if(tick_before_poll!=0 && timeout==0) {
> +               tick_before_poll--;
> +               goto ltick_before_poll;
> +       }
> +       tick_before_poll=TICKS_BEFORE_POLL;
>         /* poll any events */
>         /* XXX: separate device handlers from system ones */
>         pf = ufds;
> @@ -1741,6 +1749,7 @@
>         }
>  #endif
> 
> +       ltick_before_poll:
>  #endif
> 
>         if (vm_running) {
> @@ -1750,10 +1759,18 @@
>             if (audio_enabled) {
>                 /* XXX: add explicit timer */
>                 SB16_run();
> -           }
> +               DMA_run();
> +           } else {
> +               int i;
> 
> -           /* run dma transfers, if any */
> -           DMA_run();
> +               /* run dma transfers, if any */
> +               for(i = 0; i < MAX_FD; i++) {
> +                       if(fd_table[i]) {
> +                               DMA_run();
> +                               break;
> +                       }
> +               }
> +           }
>         }
> 
>         /* real time timers */
> 
> 
> --w
> vodz
> 
> 
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