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doc: mention async link latency in latency doc

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Wim Taymans 2025-09-16 14:09:08 +02:00
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39
doc/dox/internals/latency.dox
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@ -100,6 +100,20 @@ When the ProcessLatency changes, the procedure to notify of latency changes is:
PipeWire will automatically aggregate latency from links and propagate the new latencies
down and upstream.
# Async nodes
When a node has the node.async property set to true, it will be considered an async
node and will be scheduled differently, see scheduling.dox.
A link between a port of an async node and another port (async or not) is called an
async link and will have the link.async=true property.
An async link will add 1 quantum of latency between the nodes it links. A special
exception is made for the output ports of the driver node, which do not add latency.
The Latency param will be updated with 1 extra quantum when they travel over an async
link.
# Examples
## A source node with a given ProcessLatency
@ -240,4 +254,29 @@ We also see that node.FL has different min/max-rate input latencies. This inform
used to insert a delay node to align the latencies again. For example, if we delay the signal
between node.FL and FL.sink with 1536 samples, the latencies will be aligned again.
## An async output stream and sink node linked together
The sink has 1 quantum of Input latency. The stream has no output latency. When the Input latency
travels over the async link 1 quantum of latency is added and the Input latency on the stream is
now 2 quanta. Similar for the stream Output latency that receives an additional 1 quantum of
latency when it arrives in the sink over the async link.
```
Latency: [{ "direction": "output", "min-quantum": 0, "max-quantum": 0 } ]
Latency: [{ "direction": "input", "min-quantum": 2, "max-quantum": 2 } ]
^
| Latency: [{ "direction": "output", "min-quantum": 1, "max-quantum": 1 } ]
| Latency: [{ "direction": "input", "min-quantum": 1, "max-quantum": 1 } ]
| |
+----------+v v+--------+
| async FL ------------ FL |
| stream + | sink |
| FR --+ FR |
+----------+ | +--------+
v
Latency: [{ "direction": "output", "min-quantum": 0, "max-quantum": 0 } ]
Latency: [{ "direction": "input", "min-quantum": 0, "max-quantum": 0 } ]
```
*/