[pulseaudio-discuss] [PATCH] echo-cancel: Try to minimise in-flight chunks in snapshot latency

[Georg Chini]

On 20.03.2017 08:25, Arun Raghavan wrote:
>
> On Thu, 9 Mar 2017, at 09:53 PM, Georg Chini wrote:
>> On 09.03.2017 17:14, Georg Chini wrote:
>>> On 09.03.2017 16:33, Arun Raghavan wrote:
>>>> On Thu, 9 Mar 2017, at 03:27 PM, Georg Chini wrote:
>>>>> On 09.03.2017 05:37, Arun Raghavan wrote:
>>>>>> We don't always know whether the in-flight memory chunks will be
>>>>>> rendered or skipped (if the source is not in RUNNING). This can
>>>>>> cause us
>>>>>> to have an erroneous estimate of drift, particularly when the
>>>>>> canceller
>>>>>> starts.
>>>>>>
>>>>>> To avoid this, we explicitly flush out the send and receive sides
>>>>>> of the
>>>>>> message queue of audio chunks going from the sink to the source before
>>>>>> trying to perform a resync.
>>>>>> ---
>>>>>>     src/modules/echo-cancel/module-echo-cancel.c | 7 ++++++-
>>>>>>     1 file changed, 6 insertions(+), 1 deletion(-)
>>>>>>
>>>>>> diff --git a/src/modules/echo-cancel/module-echo-cancel.c
>>>>>> b/src/modules/echo-cancel/module-echo-cancel.c
>>>>>> index dfd05b6..ed75e0c 100644
>>>>>> --- a/src/modules/echo-cancel/module-echo-cancel.c
>>>>>> +++ b/src/modules/echo-cancel/module-echo-cancel.c
>>>>>> @@ -683,8 +683,13 @@ static void do_resync(struct userdata *u) {
>>>>>>         pa_log("Doing resync");
>>>>>>            /* update our snapshot */
>>>>>> -    source_output_snapshot_within_thread(u, &latency_snapshot);
>>>>>> +    /* 1. Get sink input latency snapshot, might cause buffers to
>>>>>> be sent to source thread */
>>>>>> pa_asyncmsgq_send(u->sink_input->sink->asyncmsgq,
>>>>>> PA_MSGOBJECT(u->sink_input), SINK_INPUT_MESSAGE_LATENCY_SNAPSHOT,
>>>>>> &latency_snapshot, 0, NULL);
>>>>>> +    /* 2. Pick up any in-flight buffers (and discard if needed) */
>>>>>> +    while (pa_asyncmsgq_process_one(u->asyncmsgq))
>>>>>> +        ;
>>>>>> +    /* 3. Now get the source output latency snapshot */
>>>>>> +    source_output_snapshot_within_thread(u, &latency_snapshot);
>>>>>>            /* calculate drift between capture and playback */
>>>>>>         diff_time = calc_diff(u, &latency_snapshot);
>>>>> While taking a look at the patch I noticed something else in the
>>>>> do_resync().
>>>>> You are doing:
>>>>>
>>>>>        source_output_snapshot_within_thread(u, &latency_snapshot);
>>>>> pa_asyncmsgq_send(u->sink_input->sink->asyncmsgq,
>>>>> PA_MSGOBJECT(u->sink_input), SINK_INPUT_MESSAGE_LATENCY_SNAPSHOT,
>>>>> &latency_snapshot, 0, NULL);
>>>>>
>>>>> from the source thread. I tried something similar in module loopback
>>>>> and
>>>>> found that you should not send a message to the sink thread from there.
>>>>>
>>>>> At least for bluetooth it looks like input and output is done in the
>>>>> same thread,
>>>>> so the pa_asyncmsg_send() will hang. I tested it with my headset and it
>>>>> hangs
>>>>> indeed.
>>>> Interesting. Do you mean for HSP, or HFP, or ...?
>>>>
>>>> -- Arun
>>> HSP, native backend. As I said, I had the same problem in
>>> module-loopback.
>> This was the command I issued:
>>
>> pacmd load-module module-echo-cancel source_name=echo_cancel_source
>> sink_name=echo_cancel_sink aec_method=webrtc use_volume_sharing=false
>> adjust_time=2 sink_master=bluez_sink.0C_E0_E4_31_23_2D.headset_head_unit
>> source_master=bluez_source.0C_E0_E4_31_23_2D.headset_head_unit
>>
>> After that you had to kill pulseaudio with kill -9.
> So you're right of course. However, the problem itself predates the
> patch, so I'd like to decouple the review of this with fixing the issues
> of sink and source being on the same thread.
>
> I'm not sure what we should be doing there. Maybe a check to compare
> asyncmsgq of the sink input with pa_thread_mq_get(), and if they're the
> same, call an _in_thread() version of get sink latency snapshot.
>
> -- Arun
Hi,

sorry for the late reply, I have been extremely busy the last two weeks.
Can't you move the while (pa_asyncmsgq_process_one(u->asyncmsgq))
into source_output_snapshot_within_thread() and call do_resync() from
the main thread?

Regards
              Georg