From: Andreas Pape apape@de.adit-jv.com
mmapped capture access on some plugins can fetch data from slave in the 'background'. A subsequent snd_pcm_wait waits for too long time to reach avail_min threshold again. Waiting too long leads to xruns on other devices waiting for the capture data.
As a fix the avail_min on slave is recalculated dynamically.
Signed-off-by: Andreas Pape apape@de.adit-jv.com Signed-off-by: Jiada Wang jiada_wang@mentor.com --- src/pcm/pcm_plugin.c | 48 +++++++++++++++++++++++++++++++++++++++++++++++- 1 file changed, 47 insertions(+), 1 deletion(-)
diff --git a/src/pcm/pcm_plugin.c b/src/pcm/pcm_plugin.c index e53c5bb..c78316b 100644 --- a/src/pcm/pcm_plugin.c +++ b/src/pcm/pcm_plugin.c @@ -535,6 +535,52 @@ static int snd_pcm_plugin_status(snd_pcm_t *pcm, snd_pcm_status_t * status) return 0; }
+static int snd_pcm_plugin_may_wait_for_avail_min(snd_pcm_t *pcm, snd_pcm_uframes_t avail) +{ + if (pcm->stream == SND_PCM_STREAM_CAPTURE && + pcm->access != SND_PCM_ACCESS_RW_INTERLEAVED && + pcm->access != SND_PCM_ACCESS_RW_NONINTERLEAVED) { + /* mmap access on capture device already consumes data from slave in avail_update operation (@see snd_pcm_plugin_avail_update). + Entering snd_pcm_wait after having already consumed some fragments leads to waiting for too long time, + as slave will unnecessarily wait for avail_min condition reached again. + To avoid unnecessary wait times we adapt the avail_min threshold on slave dynamically. + Just modifying slave->avail_min as a shortcut and lightweight solution does not work for all slave plugin types + and in addition it will not propagate the change through all downstream plugins, so we have to use the sw_params API. + note: reading fragmental parts from slave will only happen in case + a) the slave can provide contineous hw_ptr between periods + b) avail_min does not match one slave_period + */ + snd_pcm_plugin_t *plugin = pcm->private_data; + snd_pcm_t *slave = plugin->gen.slave; + snd_pcm_uframes_t needed_slave_avail_min; + snd_pcm_sframes_t available; + + /* update, as it might have changed. This will also call avail_update on slave and also can return error*/ + available = snd_pcm_avail_update(pcm); + if (available < 0) + return 0; + + if (available >= pcm->avail_min) + /*don't wait at all. As we can't configure avail_min of slave to 0 return here*/ + return 0; + + needed_slave_avail_min = pcm->avail_min - available; + if (slave->avail_min != needed_slave_avail_min) { + snd_pcm_sw_params_t *swparams; + snd_pcm_sw_params_alloca(&swparams); + /* pray that changing sw_params while running is properly implemented in all downstream plugins... it's legal but not commonly used.*/ + snd_pcm_sw_params_current(slave, swparams); + /* snd_pcm_sw_params_set_avail_min() restricts setting to >= period size. + This conflicts at least with our dshare patch which allows combining multiple periods or with slaves which return hw postions between periods + -> set directly in sw_param structure */ + swparams->avail_min = needed_slave_avail_min; + snd_pcm_sw_params(slave, swparams); + } + avail = available; + } + return snd_pcm_generic_may_wait_for_avail_min(pcm, avail); +} + const snd_pcm_fast_ops_t snd_pcm_plugin_fast_ops = { .status = snd_pcm_plugin_status, .state = snd_pcm_generic_state, @@ -564,7 +610,7 @@ const snd_pcm_fast_ops_t snd_pcm_plugin_fast_ops = { .poll_descriptors_count = snd_pcm_generic_poll_descriptors_count, .poll_descriptors = snd_pcm_generic_poll_descriptors, .poll_revents = snd_pcm_generic_poll_revents, - .may_wait_for_avail_min = snd_pcm_generic_may_wait_for_avail_min, + .may_wait_for_avail_min = snd_pcm_plugin_may_wait_for_avail_min, };
#endif