The branch main has been updated by christos:
URL:
https://cgit.FreeBSD.org/src/commit/?id=b2e97edffdab6ad1e9103a6bbe90300d78a961ed
commit b2e97edffdab6ad1e9103a6bbe90300d78a961ed
Author: Florian Walpen <d...@submerge.ch>
AuthorDate: 2024-02-12 11:04:57 +0000
Commit: Christos Margiolis <chris...@freebsd.org>
CommitDate: 2024-02-12 11:06:19 +0000
snd_uaudio(4): Adapt buffer length to buffer_ms tunable.
Adapt the length of the driver side audio buffer to the USB transfer
interval, which is adjustable through the buffer_ms tunable. This
eliminates unnecessary latency in USB audio playback.
To reduce power consumption caused by frequent CPU wakeups, increase the
default buffer_ms value to 4ms. In combination with adaptive buffer
length, this still results in less roundtrip latency compared to the
previous 2ms default.
Extend the buffer_ms value range to 1ms for low latency applications.
MFC after: 2 weeks
Reviewed by: christos
Differential Revision: https://reviews.freebsd.org/D41942
---
sys/dev/sound/usb/uaudio.c | 70 +++++++++++++++++++++++++++++++++++++++-------
1 file changed, 60 insertions(+), 10 deletions(-)
diff --git a/sys/dev/sound/usb/uaudio.c b/sys/dev/sound/usb/uaudio.c
index 917b6bd3f238..b0bf815f7797 100644
--- a/sys/dev/sound/usb/uaudio.c
+++ b/sys/dev/sound/usb/uaudio.c
@@ -96,7 +96,7 @@
static int uaudio_default_rate = 0; /* use rate list */
static int uaudio_default_bits = 32;
static int uaudio_default_channels = 0; /* use default */
-static int uaudio_buffer_ms = 2;
+static int uaudio_buffer_ms = 4;
static bool uaudio_handle_hid = true;
static SYSCTL_NODE(_hw_usb, OID_AUTO, uaudio, CTLFLAG_RW | CTLFLAG_MPSAFE, 0,
@@ -110,6 +110,9 @@ SYSCTL_INT(_hw_usb_uaudio, OID_AUTO, default_bits,
CTLFLAG_RWTUN,
SYSCTL_INT(_hw_usb_uaudio, OID_AUTO, default_channels, CTLFLAG_RWTUN,
&uaudio_default_channels, 0, "uaudio default sample channels");
+#define UAUDIO_BUFFER_MS_MIN 1
+#define UAUDIO_BUFFER_MS_MAX 8
+
static int
uaudio_buffer_ms_sysctl(SYSCTL_HANDLER_ARGS)
{
@@ -121,10 +124,10 @@ uaudio_buffer_ms_sysctl(SYSCTL_HANDLER_ARGS)
if (err != 0 || req->newptr == NULL || val == uaudio_buffer_ms)
return (err);
- if (val > 8)
- val = 8;
- else if (val < 2)
- val = 2;
+ if (val > UAUDIO_BUFFER_MS_MAX)
+ val = UAUDIO_BUFFER_MS_MAX;
+ else if (val < UAUDIO_BUFFER_MS_MIN)
+ val = UAUDIO_BUFFER_MS_MIN;
uaudio_buffer_ms = val;
@@ -133,7 +136,7 @@ uaudio_buffer_ms_sysctl(SYSCTL_HANDLER_ARGS)
SYSCTL_PROC(_hw_usb_uaudio, OID_AUTO, buffer_ms,
CTLTYPE_INT | CTLFLAG_RWTUN | CTLFLAG_MPSAFE, 0, sizeof(int),
uaudio_buffer_ms_sysctl, "I",
- "uaudio buffering delay from 2ms to 8ms");
+ "uaudio buffering delay in milliseconds, from 1 to 8");
#ifdef USB_DEBUG
static int uaudio_debug;
@@ -1310,13 +1313,60 @@ uaudio_detach(device_t dev)
return (0);
}
+static uint32_t
+uaudio_get_interval_frames(const usb_endpoint_descriptor_audio_t *ed)
+{
+ uint32_t frames = 1;
+ /* Isochronous transfer interval is 2^(bInterval - 1) frames. */
+ if (ed->bInterval >= 1 && ed->bInterval <= 16)
+ frames = (1 << (ed->bInterval - 1));
+ /* Limit transfer interval to maximum number of frames. */
+ if (frames > UAUDIO_NFRAMES)
+ frames = UAUDIO_NFRAMES;
+ return (frames);
+}
+
+static uint32_t
+uaudio_get_buffer_ms(struct uaudio_softc *sc, uint32_t int_frames)
+{
+ uint32_t ms = 1;
+ uint32_t fps = usbd_get_isoc_fps(sc->sc_udev);
+ /* Make sure a whole USB transfer interval fits into the buffer. */
+ if (fps >= 1000 && int_frames > 0 && int_frames <= UAUDIO_NFRAMES) {
+ /* Convert interval frames to milliseconds. */
+ ms = ((int_frames * 1000) / fps);
+ }
+ /* Respect minimum buffer length set through buffer_ms tunable. */
+ if (ms < uaudio_buffer_ms)
+ ms = uaudio_buffer_ms;
+ /* Limit buffer length to 8 milliseconds. */
+ if (ms > UAUDIO_BUFFER_MS_MAX)
+ ms = UAUDIO_BUFFER_MS_MAX;
+ return (ms);
+}
+
static uint32_t
uaudio_get_buffer_size(struct uaudio_chan *ch, uint8_t alt)
{
struct uaudio_chan_alt *chan_alt = &ch->usb_alt[alt];
- /* We use 2 times 8ms of buffer */
- uint32_t buf_size = chan_alt->sample_size *
- howmany(chan_alt->sample_rate * (UAUDIO_NFRAMES / 8), 1000);
+ uint32_t int_frames, ms, buf_size;
+ /* USB transfer interval in frames, from endpoint descriptor. */
+ int_frames = uaudio_get_interval_frames(chan_alt->p_ed1);
+ /* Buffer length in milliseconds, and in bytes of audio data. */
+ ms = uaudio_get_buffer_ms(ch->priv_sc, int_frames);
+ buf_size = chan_alt->sample_size *
+ howmany(chan_alt->sample_rate * ms, 1000);
+ return (buf_size);
+}
+
+static uint32_t
+uaudio_max_buffer_size(struct uaudio_chan *ch, uint8_t alt)
+{
+ struct uaudio_chan_alt *chan_alt = &ch->usb_alt[alt];
+ uint32_t buf_size;
+ /* Maximum buffer length is 8 milliseconds. */
+ buf_size = chan_alt->sample_size *
+ howmany(chan_alt->sample_rate * UAUDIO_BUFFER_MS_MAX, 1000);
return (buf_size);
}
@@ -2626,7 +2676,7 @@ uaudio_chan_init(struct uaudio_chan *ch, struct snd_dbuf
*b,
buf_size = 0;
for (x = 0; x != ch->num_alt; x++) {
- uint32_t temp = uaudio_get_buffer_size(ch, x);
+ uint32_t temp = uaudio_max_buffer_size(ch, x);
if (temp > buf_size)
buf_size = temp;
}
