audio: Reset rate control when adding bytes

Commit 90320051ea99 ("spiceaudio: add a pcm_ops buffer_get_free
function") caused to emit messages saying "Resetting rate control"
frequently when the guest generates no frames.

audio_rate_peek_bytes() resets the rate control when frames < 0 ||
frames > 65536 where frames is the rate-limited number of frames.
Resetting when frames < 0 is sensible as the number simply doesn't make
sense.

There is a problem when frames > 65536. It implies the guest stopped
generating frames for a while so it makes sense to reset the rate
control when the guest resumed generating frames. However, the
commit mentioned earlier broke this assumption by letting spiceaudio
call audio_rate_peek_bytes() whether the guest is generating frames or
not.

Reset the rate control in audio_rate_add_bytes(), which is called only
when actually adding frames, according to the previous call to
audio_rate_peek_bytes() to avoid frequent rate control resets even when
the guest generates no frame.

Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
Message-Id: <20250317-rate-v1-1-da9df062747c@daynix.com>

2 files changed, 9 insertions, 6 deletions

diff --git a/audio/audio.c b/audio/audio.c
index b58ad74..89f091b 100644
--- a/audio/audio.c
+++ b/audio/audio.c
@@ -2283,17 +2283,19 @@ size_t audio_rate_peek_bytes(RateCtl *rate, struct audio_pcm_info *info)
     ticks = now - rate->start_ticks;
     bytes = muldiv64(ticks, info->bytes_per_second, NANOSECONDS_PER_SECOND);
     frames = (bytes - rate->bytes_sent) / info->bytes_per_frame;
-    if (frames < 0 || frames > 65536) {
-        AUD_log(NULL, "Resetting rate control (%" PRId64 " frames)\n", frames);
-        audio_rate_start(rate);
-        frames = 0;
-    }
+    rate->peeked_frames = frames;
 
-    return frames * info->bytes_per_frame;
+    return frames < 0 ? 0 : frames * info->bytes_per_frame;
 }
 
 void audio_rate_add_bytes(RateCtl *rate, size_t bytes_used)
 {
+    if (rate->peeked_frames < 0 || rate->peeked_frames > 65536) {
+        AUD_log(NULL, "Resetting rate control (%" PRId64 " frames)\n",
+                rate->peeked_frames);
+        audio_rate_start(rate);
+    }
+
     rate->bytes_sent += bytes_used;
 }
 
diff --git a/audio/audio_int.h b/audio/audio_int.h
index 2d079d0..f78ca05 100644
--- a/audio/audio_int.h
+++ b/audio/audio_int.h
@@ -255,6 +255,7 @@ const char *audio_application_name(void);
 typedef struct RateCtl {
     int64_t start_ticks;
     int64_t bytes_sent;
+    int64_t peeked_frames;
 } RateCtl;
 
 void audio_rate_start(RateCtl *rate);