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85 lines
3.5 KiB
Text
85 lines
3.5 KiB
Text
Fixing Performance
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1) Observations
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The following observations are made when considering the current (17/11/2004)
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problems in gstreamer.
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- startup time.
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Most of the time is spend in reading the xml registry. Several methods exist
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for not using a registry (see testsuite/plugin/).
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Since registries are pluggable, one can also write a binary registry which
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should significantly reduce the size and the load time.
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- Performance in state changes
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State changes are pretty heavy currently because negotiation happens at
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each state change. The PAUSED->PLAYING state change in particular is
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too heavy and should be made more 'snappy'.
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- Performance in data passing.
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Too much checking is done in the push/pull functions. Most of these checks
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can be performed more efficiently in the plugins, like checking if the
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element is sufficiently negotiated. The discont event 'invent' hack used
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for fixing the synchronisation has to go away.
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We also propose a get_range based method for pads so that random-access
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in file-based sources can happen more efficiently (typical for muxers).
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- Scheduling overhead.
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The current default opt scheduler has extensive data-structures and does
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uses fairly complicated algorithms for grouping and scheduling elements.
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This has performance impact on pipeline constructions and pipeline
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execution.
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- Events in dataflow.
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Because events are put inside the dataflow, a typical chain function has
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to check if the GstData object is an event of a buffer.
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2) Proposed solutions
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- startup time.
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Volunteers to implement a binary registry?
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- The changes listed in the separate document 'threading' will greatly
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reduce the number of negotiation steps during state changes. It will
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also reduce the latency between PAUSED<->PLAYING since it basically
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involves unlocking a mutex in the sinks.
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- adding return values to push/pull will offload some checks to the plugins
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that can more efficiently and more accuratly handle most error cases.
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With the new sync model in 'threading' it is also not needed to have
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the 'invented' events in the pull function.
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- The following scheduling policies should be made possible for pads:
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1) get_range <-> pull-range-based
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2) get <-> pull based
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3) push <-> chain-based
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The scheduling policies are listed in order of preference. A pad should
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export what scheduling it supports and the core will select what
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scheduling method to use. It is possible for a pad to support more than
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one scheduling method.
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It is possible that two elements cannot connect when they do not support
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compatible scheduling policies. We require that pull-based pads also
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support the chain based methods, at minimal, using a helper function to
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queue a buffer and that get-based pads also support a push based implementation.
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- With the changes listed in 'threading' the scheduler will be a lot more
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simple since it does not have to keep track of groups and connected
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elements. Starting and scheduling the pipeline will be a matter of
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starting the source/loop GstTasks and they will from there on take
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over.
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- move events out of the dataflow. Different methods will be used to
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send/receive events. This will also remove some of the checks in
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the push/pull functions. Note that plugins are still able to serialize
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buffers and events because they hold the streaming lock.
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3) detailed explanation
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TO BE WRITTEN
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