Re: [Qemu-devel] [PATCH] cuda: decrease time delay before raising VIA SR interrupt

[Philippe Mathieu-Daudé]

Hi Mark,

On 2/10/19 6:44 PM, Mark Cave-Ayland wrote:
> In order to handle a race condition in MacOS 9, a delay was introduced when
> raising the VIA SR interrupt inspired by similar code in MacOnLinux.
> 
> During original testing of the MacOS 9 patches it was found that the 30us
> delay used in MacOnLinux did not work reliably within QEMU, and a value of
> 300us was required to function correctly.
> 
> Recent experiments have shown that the previous reliability issues are no
> longer present, and this value can be reduced down to 20us with no apparent
> ill effects in my local tests. This has the benefit of considerably improving
> the responsiveness of the ADB keyboard and mouse with the guest.
> 
> Signed-off-by: Mark Cave-Ayland <address@hidden>
> ---
>  hw/misc/macio/cuda.c | 11 +----------
>  1 file changed, 1 insertion(+), 10 deletions(-)
> 
> diff --git a/hw/misc/macio/cuda.c b/hw/misc/macio/cuda.c
> index c4f7a2f39b..3febacdd1e 100644
> --- a/hw/misc/macio/cuda.c
> +++ b/hw/misc/macio/cuda.c
> @@ -97,17 +97,8 @@ static void cuda_set_sr_int(void *opaque)
>  
>  static void cuda_delay_set_sr_int(CUDAState *s)
>  {
> -    MOS6522CUDAState *mcs = &s->mos6522_cuda;
> -    MOS6522State *ms = MOS6522(mcs);
> -    MOS6522DeviceClass *mdc = MOS6522_DEVICE_GET_CLASS(ms);
>      int64_t expire;
>  
> -    if (ms->dirb == 0xff || s->sr_delay_ns == 0) {
> -        /* Disabled or not in Mac OS, fire the IRQ directly */
> -        mdc->set_sr_int(ms);
> -        return;
> -    }

The change of sr_delay_ns below is well explained, but I don't
understand why you remove the previous if().

> -
>      trace_cuda_delay_set_sr_int();
>  
>      expire = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) + s->sr_delay_ns;
> @@ -542,7 +533,7 @@ static void cuda_realize(DeviceState *dev, Error **errp)
>      s->tick_offset = (uint32_t)mktimegm(&tm) + RTC_OFFSET;
>  
>      s->sr_delay_timer = timer_new_ns(QEMU_CLOCK_VIRTUAL, cuda_set_sr_int, s);
> -    s->sr_delay_ns = 300 * SCALE_US;
> +    s->sr_delay_ns = 20 * SCALE_US;
>  
>      s->adb_poll_timer = timer_new_ns(QEMU_CLOCK_VIRTUAL, cuda_adb_poll, s);
>      s->adb_poll_mask = 0xffff;
>