I wrote:
This (untested) patch tries to avoid too many busy looping.
Oops, off-by-one error (avail == avail_min should not wait).
Regards, Clemens
--- a/sound/core/pcm_lib.c +++ b/sound/core/pcm_lib.c @@ -1894,7 +1894,7 @@ static snd_pcm_sframes_t snd_pcm_lib_write1(struct snd_pcm_substream *substream, struct snd_pcm_runtime *runtime = substream->runtime; snd_pcm_uframes_t xfer = 0; snd_pcm_uframes_t offset = 0; - int err = 0; + int busy_loops = 0, err = 0;
if (size == 0) return 0; @@ -1919,12 +1919,17 @@ static snd_pcm_sframes_t snd_pcm_lib_write1(struct snd_pcm_substream *substream, runtime->twake = runtime->control->avail_min ? : 1; while (size > 0) { snd_pcm_uframes_t frames, appl_ptr, appl_ofs; - snd_pcm_uframes_t avail; + snd_pcm_uframes_t avail, avail_nowait_min; snd_pcm_uframes_t cont; + + if (busy_loops < 5) + avail_nowait_min = 1; + else + avail_nowait_min = min(runtime->control->avail_min, size); if (runtime->status->state == SNDRV_PCM_STATE_RUNNING) snd_pcm_update_hw_ptr(substream); avail = snd_pcm_playback_avail(runtime); - if (!avail) { + if (avail < avail_nowait_min) { if (nonblock) { err = -EAGAIN; goto _end_unlock; @@ -1934,6 +1939,9 @@ static snd_pcm_sframes_t snd_pcm_lib_write1(struct snd_pcm_substream *substream, err = wait_for_avail(substream, &avail); if (err < 0) goto _end_unlock; + busy_loops = 0; + } else { + busy_loops++; } frames = size > avail ? avail : size; cont = runtime->buffer_size - runtime->control->appl_ptr % runtime->buffer_size;