Improve scalability in task_group #1310
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Signed-off-by: pavelkumbrasev <pavel.kumbrasev@intel.com>
Signed-off-by: pavelkumbrasev <pavel.kumbrasev@intel.com>
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Signed-off-by: pavelkumbrasev <pavel.kumbrasev@intel.com>
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include/oneapi/tbb/task_group.h
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| template<typename F> | ||
| class function_task : public task { | ||
| const F m_func; | ||
| class task_group_continuation { |
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Why is it called continuation, while it is clearly does the reference management only?
Continuation has always been a task that executes after its child tasks have been completed.
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This code will be executed after all the children tasks so technically it is still a continuation :)
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If I get it right, you suggesting to call the first task a "task" and all the tasks that will execute after it a "continuation". Right? Sounds bad to me...
I agree that it can be a name for a local variable, but I don't think it can be a name for the whole class.
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Please consider to rename into distributed_reference_counter
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Description
task_group has a flat reference counting scheme i.e., there is a central reference counter where all the created tasks should increase/decrease reference during execution.
This approach works fine while tasks are big and submitted from small number of threads (<8).
When multiple threads will start tree-like algorithm with a lot of tasks the overall performance of the application will drastically degrade with increasing number of threads due to huge synchronization cost.
This patch introduce tree-like scheme in task_group i.e., if nesting is detected continuation will be created and nested tasks will work with reference counter of this newly created continuation instead task_group reference counter.
This process of continuation creation will repeat itself each time nesting is detected.
Fixes #313
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