[alsa-devel] Buffer size for ALSA USB PCM audio
Daniel Mack
zonque at gmail.com
Mon Sep 9 16:20:28 CEST 2013
On 28.08.2013 20:46, Alan Stern wrote:
> On Wed, 28 Aug 2013, Clemens Ladisch wrote:
>
>> Sorry, what I said applies more to explicit sync endpoints. When using
>> implicit sync, a playback URB is submitted for each completed capture
>> URB, with the number of samples per packet identical to the
>> corresponding capture packet, so the parameters must be identical.
>
> Got it. Below is an updated patch.
>
> James, the problem you encountered was most likely a result of the
> faulty treatment of capture endpoints that Clemens pointed out. It was
> quite obvious in the usbmon traces that the unpatched driver used 8
> packets per URB whereas the patched driver used 22. This updated patch
> should fix that problem.
I gave this patch a try and I can confirm that it results in a
sigificant improvement for small sample buffers.
So feel free to add my
Tested-by: Daniel Mack <zonque at gmail.com>
Thanks,
Daniel
> Index: usb-3.11/sound/usb/usbaudio.h
> ===================================================================
> --- usb-3.11.orig/sound/usb/usbaudio.h
> +++ usb-3.11/sound/usb/usbaudio.h
> @@ -55,7 +55,6 @@ struct snd_usb_audio {
> struct list_head mixer_list; /* list of mixer interfaces */
>
> int setup; /* from the 'device_setup' module param */
> - int nrpacks; /* from the 'nrpacks' module param */
> bool autoclock; /* from the 'autoclock' module param */
>
> struct usb_host_interface *ctrl_intf; /* the audio control interface */
> Index: usb-3.11/sound/usb/card.c
> ===================================================================
> --- usb-3.11.orig/sound/usb/card.c
> +++ usb-3.11/sound/usb/card.c
> @@ -79,7 +79,6 @@ static bool enable[SNDRV_CARDS] = SNDRV_
> /* Vendor/product IDs for this card */
> static int vid[SNDRV_CARDS] = { [0 ... (SNDRV_CARDS-1)] = -1 };
> static int pid[SNDRV_CARDS] = { [0 ... (SNDRV_CARDS-1)] = -1 };
> -static int nrpacks = 8; /* max. number of packets per urb */
> static int device_setup[SNDRV_CARDS]; /* device parameter for this card */
> static bool ignore_ctl_error;
> static bool autoclock = true;
> @@ -94,8 +93,6 @@ module_param_array(vid, int, NULL, 0444)
> MODULE_PARM_DESC(vid, "Vendor ID for the USB audio device.");
> module_param_array(pid, int, NULL, 0444);
> MODULE_PARM_DESC(pid, "Product ID for the USB audio device.");
> -module_param(nrpacks, int, 0644);
> -MODULE_PARM_DESC(nrpacks, "Max. number of packets per URB.");
> module_param_array(device_setup, int, NULL, 0444);
> MODULE_PARM_DESC(device_setup, "Specific device setup (if needed).");
> module_param(ignore_ctl_error, bool, 0444);
> @@ -374,7 +371,6 @@ static int snd_usb_audio_create(struct u
> chip->dev = dev;
> chip->card = card;
> chip->setup = device_setup[idx];
> - chip->nrpacks = nrpacks;
> chip->autoclock = autoclock;
> chip->probing = 1;
>
> @@ -756,10 +752,6 @@ static struct usb_driver usb_audio_drive
>
> static int __init snd_usb_audio_init(void)
> {
> - if (nrpacks < 1 || nrpacks > MAX_PACKS) {
> - printk(KERN_WARNING "invalid nrpacks value.\n");
> - return -EINVAL;
> - }
> return usb_register(&usb_audio_driver);
> }
>
> Index: usb-3.11/sound/usb/endpoint.h
> ===================================================================
> --- usb-3.11.orig/sound/usb/endpoint.h
> +++ usb-3.11/sound/usb/endpoint.h
> @@ -12,6 +12,8 @@ int snd_usb_endpoint_set_params(struct s
> snd_pcm_format_t pcm_format,
> unsigned int channels,
> unsigned int period_bytes,
> + unsigned int period_frames,
> + unsigned int buffer_periods,
> unsigned int rate,
> struct audioformat *fmt,
> struct snd_usb_endpoint *sync_ep);
> Index: usb-3.11/sound/usb/card.h
> ===================================================================
> --- usb-3.11.orig/sound/usb/card.h
> +++ usb-3.11/sound/usb/card.h
> @@ -2,11 +2,11 @@
> #define __USBAUDIO_CARD_H
>
> #define MAX_NR_RATES 1024
> -#define MAX_PACKS 20
> +#define MAX_PACKS 6 /* per URB */
> #define MAX_PACKS_HS (MAX_PACKS * 8) /* in high speed mode */
> -#define MAX_URBS 8
> +#define MAX_URBS 12
> #define SYNC_URBS 4 /* always four urbs for sync */
> -#define MAX_QUEUE 24 /* try not to exceed this queue length, in ms */
> +#define MAX_QUEUE 18 /* try not to exceed this queue length, in ms */
>
> struct audioformat {
> struct list_head list;
> @@ -87,6 +87,7 @@ struct snd_usb_endpoint {
> unsigned int phase; /* phase accumulator */
> unsigned int maxpacksize; /* max packet size in bytes */
> unsigned int maxframesize; /* max packet size in frames */
> + unsigned int max_urb_frames; /* max URB size in frames */
> unsigned int curpacksize; /* current packet size in bytes (for capture) */
> unsigned int curframesize; /* current packet size in frames (for capture) */
> unsigned int syncmaxsize; /* sync endpoint packet size */
> @@ -116,6 +117,8 @@ struct snd_usb_substream {
> unsigned int channels_max; /* max channels in the all audiofmts */
> unsigned int cur_rate; /* current rate (for hw_params callback) */
> unsigned int period_bytes; /* current period bytes (for hw_params callback) */
> + unsigned int period_frames; /* current frames per period */
> + unsigned int buffer_periods; /* current periods per buffer */
> unsigned int altset_idx; /* USB data format: index of alternate setting */
> unsigned int txfr_quirk:1; /* allow sub-frame alignment */
> unsigned int fmt_type; /* USB audio format type (1-3) */
> @@ -125,6 +128,7 @@ struct snd_usb_substream {
>
> unsigned int hwptr_done; /* processed byte position in the buffer */
> unsigned int transfer_done; /* processed frames since last period update */
> + unsigned int frame_limit; /* limits number of packets in URB */
>
> /* data and sync endpoints for this stream */
> unsigned int ep_num; /* the endpoint number */
> Index: usb-3.11/sound/usb/pcm.c
> ===================================================================
> --- usb-3.11.orig/sound/usb/pcm.c
> +++ usb-3.11/sound/usb/pcm.c
> @@ -562,6 +562,7 @@ static int configure_sync_endpoint(struc
> subs->pcm_format,
> subs->channels,
> subs->period_bytes,
> + 0, 0,
> subs->cur_rate,
> subs->cur_audiofmt,
> NULL);
> @@ -598,6 +599,7 @@ static int configure_sync_endpoint(struc
> subs->pcm_format,
> sync_fp->channels,
> sync_period_bytes,
> + 0, 0,
> subs->cur_rate,
> sync_fp,
> NULL);
> @@ -620,6 +622,8 @@ static int configure_endpoint(struct snd
> subs->pcm_format,
> subs->channels,
> subs->period_bytes,
> + subs->period_frames,
> + subs->buffer_periods,
> subs->cur_rate,
> subs->cur_audiofmt,
> subs->sync_endpoint);
> @@ -656,6 +660,8 @@ static int snd_usb_hw_params(struct snd_
>
> subs->pcm_format = params_format(hw_params);
> subs->period_bytes = params_period_bytes(hw_params);
> + subs->period_frames = params_period_size(hw_params);
> + subs->buffer_periods = params_periods(hw_params);
> subs->channels = params_channels(hw_params);
> subs->cur_rate = params_rate(hw_params);
>
> @@ -1330,6 +1336,7 @@ static void prepare_playback_urb(struct
> frames = 0;
> urb->number_of_packets = 0;
> spin_lock_irqsave(&subs->lock, flags);
> + subs->frame_limit += ep->max_urb_frames;
> for (i = 0; i < ctx->packets; i++) {
> if (ctx->packet_size[i])
> counts = ctx->packet_size[i];
> @@ -1344,6 +1351,7 @@ static void prepare_playback_urb(struct
> subs->transfer_done += counts;
> if (subs->transfer_done >= runtime->period_size) {
> subs->transfer_done -= runtime->period_size;
> + subs->frame_limit = 0;
> period_elapsed = 1;
> if (subs->fmt_type == UAC_FORMAT_TYPE_II) {
> if (subs->transfer_done > 0) {
> @@ -1366,8 +1374,10 @@ static void prepare_playback_urb(struct
> break;
> }
> }
> - if (period_elapsed &&
> - !snd_usb_endpoint_implicit_feedback_sink(subs->data_endpoint)) /* finish at the period boundary */
> + /* finish at the period boundary or after enough frames */
> + if ((period_elapsed ||
> + subs->transfer_done >= subs->frame_limit) &&
> + !snd_usb_endpoint_implicit_feedback_sink(ep))
> break;
> }
> bytes = frames * ep->stride;
> Index: usb-3.11/sound/usb/endpoint.c
> ===================================================================
> --- usb-3.11.orig/sound/usb/endpoint.c
> +++ usb-3.11/sound/usb/endpoint.c
> @@ -571,11 +571,14 @@ static int data_ep_set_params(struct snd
> snd_pcm_format_t pcm_format,
> unsigned int channels,
> unsigned int period_bytes,
> + unsigned int frames_per_period,
> + unsigned int periods_per_buffer,
> struct audioformat *fmt,
> struct snd_usb_endpoint *sync_ep)
> {
> - unsigned int maxsize, i, urb_packs, total_packs, packs_per_ms;
> - int is_playback = usb_pipeout(ep->pipe);
> + unsigned int maxsize, minsize, packs_per_ms, max_packs_per_urb;
> + unsigned int max_packs_per_period, urbs_per_period, urb_packs;
> + unsigned int max_urbs, i;
> int frame_bits = snd_pcm_format_physical_width(pcm_format) * channels;
>
> if (pcm_format == SNDRV_PCM_FORMAT_DSD_U16_LE && fmt->dsd_dop) {
> @@ -608,58 +611,67 @@ static int data_ep_set_params(struct snd
> else
> ep->curpacksize = maxsize;
>
> - if (snd_usb_get_speed(ep->chip->dev) != USB_SPEED_FULL)
> + if (snd_usb_get_speed(ep->chip->dev) != USB_SPEED_FULL) {
> packs_per_ms = 8 >> ep->datainterval;
> - else
> - packs_per_ms = 1;
> -
> - if (is_playback && !snd_usb_endpoint_implicit_feedback_sink(ep)) {
> - urb_packs = max(ep->chip->nrpacks, 1);
> - urb_packs = min(urb_packs, (unsigned int) MAX_PACKS);
> + max_packs_per_urb = MAX_PACKS_HS;
> } else {
> - urb_packs = 1;
> + packs_per_ms = 1;
> + max_packs_per_urb = MAX_PACKS;
> }
> -
> - urb_packs *= packs_per_ms;
> -
> if (sync_ep && !snd_usb_endpoint_implicit_feedback_sink(ep))
> - urb_packs = min(urb_packs, 1U << sync_ep->syncinterval);
> + max_packs_per_urb = min(max_packs_per_urb,
> + 1U << sync_ep->syncinterval);
> + max_packs_per_urb = max(1u, max_packs_per_urb >> ep->datainterval);
> +
> + /*
> + * Capture endpoints need to use small URBs because there's no way
> + * to tell in advance where the next period will end, and we don't
> + * want the next URB to complete much after the period ends.
> + *
> + * Playback endpoints with implicit sync much use the same parameters
> + * as their corresponding capture endpoint.
> + */
> + if (usb_pipein(ep->pipe) ||
> + snd_usb_endpoint_implicit_feedback_sink(ep)) {
> +
> + /* make capture URBs <= 1 ms and smaller than a period */
> + urb_packs = min(max_packs_per_urb, packs_per_ms);
> + while (urb_packs > 1 && urb_packs * maxsize >= period_bytes)
> + urb_packs >>= 1;
> + ep->nurbs = MAX_URBS;
>
> - /* decide how many packets to be used */
> - if (is_playback && !snd_usb_endpoint_implicit_feedback_sink(ep)) {
> - unsigned int minsize, maxpacks;
> + /*
> + * Playback endpoints without implicit sync are adjusted so that
> + * a period fits as evenly as possible in the smallest number of
> + * URBs. The total number of URBs is adjusted to the size of the
> + * ALSA buffer, subject to the MAX_URBS and MAX_QUEUE limits.
> + */
> + } else {
> /* determine how small a packet can be */
> - minsize = (ep->freqn >> (16 - ep->datainterval))
> - * (frame_bits >> 3);
> + minsize = (ep->freqn >> (16 - ep->datainterval)) *
> + (frame_bits >> 3);
> /* with sync from device, assume it can be 12% lower */
> if (sync_ep)
> minsize -= minsize >> 3;
> minsize = max(minsize, 1u);
> - total_packs = (period_bytes + minsize - 1) / minsize;
> - /* we need at least two URBs for queueing */
> - if (total_packs < 2) {
> - total_packs = 2;
> - } else {
> - /* and we don't want too long a queue either */
> - maxpacks = max(MAX_QUEUE * packs_per_ms, urb_packs * 2);
> - total_packs = min(total_packs, maxpacks);
> - }
> - } else {
> - while (urb_packs > 1 && urb_packs * maxsize >= period_bytes)
> - urb_packs >>= 1;
> - total_packs = MAX_URBS * urb_packs;
> - }
>
> - ep->nurbs = (total_packs + urb_packs - 1) / urb_packs;
> - if (ep->nurbs > MAX_URBS) {
> - /* too much... */
> - ep->nurbs = MAX_URBS;
> - total_packs = MAX_URBS * urb_packs;
> - } else if (ep->nurbs < 2) {
> - /* too little - we need at least two packets
> - * to ensure contiguous playback/capture
> - */
> - ep->nurbs = 2;
> + /* how many packets will contain an entire ALSA period? */
> + max_packs_per_period = DIV_ROUND_UP(period_bytes, minsize);
> +
> + /* how many URBs will contain a period? */
> + urbs_per_period = DIV_ROUND_UP(max_packs_per_period,
> + max_packs_per_urb);
> + /* how many packets are needed in each URB? */
> + urb_packs = DIV_ROUND_UP(max_packs_per_period, urbs_per_period);
> +
> + /* limit the number of frames in a single URB */
> + ep->max_urb_frames = DIV_ROUND_UP(frames_per_period,
> + urbs_per_period);
> +
> + /* try to use enough URBs to contain an entire ALSA buffer */
> + max_urbs = min((unsigned) MAX_URBS,
> + MAX_QUEUE * packs_per_ms / urb_packs);
> + ep->nurbs = min(max_urbs, urbs_per_period * periods_per_buffer);
> }
>
> /* allocate and initialize data urbs */
> @@ -667,8 +679,7 @@ static int data_ep_set_params(struct snd
> struct snd_urb_ctx *u = &ep->urb[i];
> u->index = i;
> u->ep = ep;
> - u->packets = (i + 1) * total_packs / ep->nurbs
> - - i * total_packs / ep->nurbs;
> + u->packets = urb_packs;
> u->buffer_size = maxsize * u->packets;
>
> if (fmt->fmt_type == UAC_FORMAT_TYPE_II)
> @@ -745,6 +756,8 @@ out_of_memory:
> * @pcm_format: the audio fomat.
> * @channels: the number of audio channels.
> * @period_bytes: the number of bytes in one alsa period.
> + * @period_frames: the number of frames in one alsa period.
> + * @buffer_periods: the number of periods in one alsa buffer.
> * @rate: the frame rate.
> * @fmt: the USB audio format information
> * @sync_ep: the sync endpoint to use, if any
> @@ -757,6 +770,8 @@ int snd_usb_endpoint_set_params(struct s
> snd_pcm_format_t pcm_format,
> unsigned int channels,
> unsigned int period_bytes,
> + unsigned int period_frames,
> + unsigned int buffer_periods,
> unsigned int rate,
> struct audioformat *fmt,
> struct snd_usb_endpoint *sync_ep)
> @@ -790,7 +805,8 @@ int snd_usb_endpoint_set_params(struct s
> switch (ep->type) {
> case SND_USB_ENDPOINT_TYPE_DATA:
> err = data_ep_set_params(ep, pcm_format, channels,
> - period_bytes, fmt, sync_ep);
> + period_bytes, period_frames,
> + buffer_periods, fmt, sync_ep);
> break;
> case SND_USB_ENDPOINT_TYPE_SYNC:
> err = sync_ep_set_params(ep, fmt);
>
>
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