[ALSA] usb-audio: optimize handling of capture URBs

USB generic driver
When preparing capture URBs, we don't need to stop when we cross a
period boundary because we now never handle more than one millisecond of
data per URB anyway.

When handling captured data, use an extra flag to call
snd_pcm_period_elapsed() no more than once.  This allows us to move the
period boundary checking code before the copying of the data which
avoids a second locking of the substream's lock.

Signed-off-by: Clemens Ladisch <clemens@ladisch.de>

1 files changed, 8 insertions, 18 deletions

diff --git a/sound/usb/usbaudio.c b/sound/usb/usbaudio.c
index a62d1313da17..a703d96bfcb4 100644
--- a/sound/usb/usbaudio.c
+++ b/sound/usb/usbaudio.c
@@ -311,27 +311,18 @@ static int prepare_capture_urb(snd_usb_substream_t *subs,
                                struct urb *urb)
 {
         int i, offs;
-        unsigned long flags;
         snd_urb_ctx_t *ctx = (snd_urb_ctx_t *)urb->context;
 
         offs = 0;
         urb->dev = ctx->subs->dev; /* we need to set this at each time */
-        urb->number_of_packets = 0;
-        spin_lock_irqsave(&subs->lock, flags);
         for (i = 0; i < ctx->packets; i++) {
                 urb->iso_frame_desc[i].offset = offs;
                 urb->iso_frame_desc[i].length = subs->curpacksize;
                 offs += subs->curpacksize;
-                urb->number_of_packets++;
-                subs->transfer_sched += subs->curframesize;
-                if (subs->transfer_sched >= runtime->period_size) {
-                        subs->transfer_sched -= runtime->period_size;
-                        break;
-                }
         }
-        spin_unlock_irqrestore(&subs->lock, flags);
         urb->transfer_buffer = ctx->buf;
         urb->transfer_buffer_length = offs;
+        urb->number_of_packets = ctx->packets;
 #if 0 // for check
         if (! urb->bandwidth) {
                 int bustime;
@@ -359,6 +350,7 @@ static int retire_capture_urb(snd_usb_substream_t *subs,
         unsigned char *cp;
         int i;
         unsigned int stride, len, oldptr;
+        int period_elapsed = 0;
 
         stride = runtime->frame_bits >> 3;
 
@@ -378,6 +370,10 @@ static int retire_capture_urb(snd_usb_substream_t *subs,
                 if (subs->hwptr_done >= runtime->buffer_size)
                         subs->hwptr_done -= runtime->buffer_size;
                 subs->transfer_done += len;
+                if (subs->transfer_done >= runtime->period_size) {
+                        subs->transfer_done -= runtime->period_size;
+                        period_elapsed = 1;
+                }
                 spin_unlock_irqrestore(&subs->lock, flags);
                 /* copy a data chunk */
                 if (oldptr + len > runtime->buffer_size) {
@@ -388,15 +384,9 @@ static int retire_capture_urb(snd_usb_substream_t *subs,
                 } else {
                         memcpy(runtime->dma_area + oldptr * stride, cp, len * stride);
                 }
-                /* update the pointer, call callback if necessary */
-                spin_lock_irqsave(&subs->lock, flags);
-                if (subs->transfer_done >= runtime->period_size) {
-                        subs->transfer_done -= runtime->period_size;
-                        spin_unlock_irqrestore(&subs->lock, flags);
-                        snd_pcm_period_elapsed(subs->pcm_substream);
-                } else
-                        spin_unlock_irqrestore(&subs->lock, flags);
         }
+        if (period_elapsed)
+                snd_pcm_period_elapsed(subs->pcm_substream);
         return 0;
 }