jackaudio: use more jack audio buffers

The next patch reduces the effective qemu playback buffer size
by timer-period. Increase the number of jack audio buffers by
one to preserve the total effective buffer size. The size of one
jack audio buffer is 512 samples. With audio defaults that's
512 samples / 44100 samples/s = 11.6 ms and only slightly larger
than the timer-period of 10 ms.

The larger jack audio buffer increases audio dropout safety,
because the high priority jack-audio worker threads can provide
audio data for a longer period of time as with a smaller buffer
and more audio data in the mixing engine buffer that they can't
access.

Signed-off-by: Volker Rümelin <vr_qemu@t-online.de>
Reviewed-by: Christian Schoenebeck <qemu_oss@crudebyte.com>
Message-Id: <20220301191311.26695-6-vr_qemu@t-online.de>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

audio/jackaudio.c

@@ -483,8 +483,8 @@ static int qjack_client_init(QJackClient *c)
         c->buffersize = 512;
     }
 
-    /* create a 2 period buffer */
-    qjack_buffer_create(&c->fifo, c->nchannels, c->buffersize * 2);
+    /* create a 3 period buffer */
+    qjack_buffer_create(&c->fifo, c->nchannels, c->buffersize * 3);
 
     qjack_client_connect_ports(c);
     c->state = QJACK_STATE_RUNNING;