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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 PipeWire will automatically aggregate latency from links and propagate the new latencies
down and upstream. 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 # Examples
## A source node with a given ProcessLatency ## 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 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. 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 } ]
```
*/ */