Re: [Qemu-devel] [PATCH 4/4] audio/hda: detect output buffer overruns and underruns

[KONRAD Frederic]

On 04/19/2018 03:10 PM, Gerd Hoffmann wrote:
> If some event caused some larger playback hickup the fine-grained timer
> adjust isn't able to recover.  Use a buffer overruns and underruns as
> indicator for that.  Reset timer adjust logic in case we detected one.

It seems that this patch causes big lockup of my Win10 KVM guest
when it tries to output a sound.
The three previous patches improved considerably the audio
output though!

> Signed-off-by: Gerd Hoffmann <address@hidden>
> ---
>   hw/audio/hda-codec.c  | 22 ++++++++++++++++++++++
>   hw/audio/trace-events |  2 ++
>   2 files changed, 24 insertions(+)
>
> diff --git a/hw/audio/hda-codec.c b/hw/audio/hda-codec.c
> index f6fb1d0fa0..623021b7c7 100644
> --- a/hw/audio/hda-codec.c
> +++ b/hw/audio/hda-codec.c
> @@ -261,6 +261,13 @@ static void hda_audio_input_cb(void *opaque, int avail)
>   
>       int64_t to_transfer = audio_MIN(B_SIZE - (wpos - rpos), avail);
>   
> +    if (to_transfer == 0) {
> +        /* reset timer adjust */
> +        st->buft_start = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
> +        trace_hda_audio_underrun(st->node->name);
> +        return;
> +    }
> +
>       hda_timer_sync_adjust(st, -((wpos - rpos) + to_transfer - (B_SIZE >> 1)));
>   
>       while (to_transfer) {
> @@ -325,6 +332,21 @@ static void hda_audio_output_cb(void *opaque, int avail)
>   
>       int64_t to_transfer = audio_MIN(wpos - rpos, avail);
>   
> +    if (to_transfer == 0) {
> +        /* reset timer adjust */
> +        st->buft_start = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
> +        trace_hda_audio_underrun(st->node->name);
> +        return;
> +    }

The lock happen here:

hda_audio_output_cb is called a lot and keeps running in
underrun. While the 1kHz callback is called regularly and
always "already have the data". So I wonder if the adjust here is
not confusing the 1kHz callback which refuse to get new data.

Regards,
Fred