On 28.02.2017 17:07, Tanu Kaskinen wrote:
> On Tue, 2017-02-28 at 16:30 +0100, Georg Chini wrote:
>> On 28.02.2017 16:11, Tanu Kaskinen wrote:
>>> On Mon, 2017-02-27 at 13:54 +0100, Georg Chini wrote:
>>>> case SINK_INPUT_MESSAGE_POST:
>>>>
>>>> - pa_sink_input_assert_io_context(u->sink_input);
>>>> + pa_memblockq_push_align(u->memblockq, chunk);
>>>> +
>>>> + /* If push has not been called yet, latency adjustments in sink_input_pop_cb()
>>>> + * are enabled. Disable them on first push and correct the memblockq. If pop
>>>> + * has not been called yet, wait until the pop_cb() requests the adjustment */
>>>> + if (u->output_thread_info.pop_called && (!u->output_thread_info.push_called || u->output_thread_info.pop_adjust)) {
>>>> + pa_usec_t time_delta;
>>>> +
>>>> + /* This is the source latency at the time push was called */
>>>> + time_delta = PA_PTR_TO_UINT(data);
>>>> + /* Add the time between push and post */
>>>> + time_delta += pa_rtclock_now() - offset;
>>>> + /* Add the sink latency */
>>>> + time_delta += pa_sink_get_latency_within_thread(u->sink_input->sink);
>>>> +
>>>> + /* The source latency report includes the audio in the chunk,
>>>> + * but since we already pushed the chunk to the memblockq, we need
>>>> + * to subtract the chunk size from the source latency so that it
>>>> + * won't be counted towards both the memblockq latency and the
>>>> + * source latency.
>>>> + * If the source has overrun, assume that the maximum it should have pushed is
>>>> + * one full source latency. It may still be possible that the next push also
>>>> + * contains too much data, then the resulting latency will be wrong. */
>>>> + if (pa_bytes_to_usec(chunk->length, &u->sink_input->sample_spec) > u->output_thread_info.effective_source_latency)
>>>> + time_delta = PA_CLIP_SUB(time_delta, u->output_thread_info.effective_source_latency);
>>>> + else
>>>> + time_delta = PA_CLIP_SUB(time_delta, pa_bytes_to_usec(chunk->length, &u->sink_input->sample_spec));
>>> Using effective_source_latency is starting to make some sense to me,
>>> but I think the comment is not easy to understand. Are you ok with it
>>> if I modify the comment like this:
>>>
>>> @@ -701,9 +701,18 @@ static int sink_input_process_msg_cb(pa_msgobject *obj, int code, void *data, in
>>> * to subtract the chunk size from the source latency so that it
>>> * won't be counted towards both the memblockq latency and the
>>> * source latency.
>>> - * If the source has overrun, assume that the maximum it should have pushed is
>>> - * one full source latency. It may still be possible that the next push also
>>> - * contains too much data, then the resulting latency will be wrong. */
>>> + *
>>> + * Sometimes the alsa source reports way too low latency (might
>>> + * be a bug in the alsa source code). This seems to happen when
>>> + * there's an overrun. As an attempt to detect overruns, we
>>> + * check if the chunk size is larger than the configured source
>>> + * latency. If so, we assume that the source should have pushed
>>> + * a chunk whose size equals the configured latency, so we
>>> + * modify time_delta only by that amount, which makes
>>> + * memblockq_adjust() drop more data than it would otherwise.
>>> + * This seems to work quite well, but it's possible that the
>>> + * next push also contains too much data, and in that case the
>>> + * resulting latency will be wrong. */
>>> if (pa_bytes_to_usec(chunk->length, &u->sink_input->sample_spec) > u->output_thread_info.effective_source_latency)
>>> time_delta = PA_CLIP_SUB(time_delta, u->output_thread_info.effective_source_latency);
>>> else
>>>
>> OK for me, except that "configured source latency" is somewhat misleading,
>> because we have a configured_source_latency variable which is not what we
>> are using here. I do however not know how to rephrase it without using many
>> words, so I'm OK with your comment.
> To me it seems that effective_source_latency really is the configured
> source latency. u->configured_source_latency, on the other hand, is
> actually the requested latency of the source output, which may be
> higher than the configured source latency. If something needs changing,
> I think it's the variable name. I suppose the reasoning behind the
> current variable name is that it represents the internal source latency
> configuration of module-loopback, but "configured source latency" is an
> established term that can be seen e.g. in "pactl list sources" output.
>
> I checked source.h, hoping to find a "configured_latency" field in
> pa_source, but the variable is named "requested_latency" there, which
> undermines my argument a bit... It would be nice if the term used in
> pactl and the field name in pa_source would be consistent.
>
>> I also discovered a small bug:
>> In update_latency_boundaries() I test for alsa devices with fixed
>> latency like this:
>>
>> s = pa_proplist_gets(source->proplist, PA_PROP_DEVICE_API);
>> if (pa_streq(s, "alsa"))
>> u->fixed_alsa_source = true;
>>
>> This will crash pulse, if the property is not set. It should be:
>>
>> if ((s = pa_proplist_gets(source->proplist,
>> PA_PROP_DEVICE_API))) {
>> if (pa_streq(s, "alsa"))
>> u->fixed_alsa_source = true;
>> }
>>
>> Shall I send a new version or can you fix it when pushing the patch?
> This code is from some later patch, so I can't fix it. I have now
> pushed the patch with my comment applied.
>
Thanks!
