Question regards to DFSMemoryScheduler

[t kevin]

Hi folks

I'm trying to understand some implementation details of xla.

https://github.com/tensorflow/tensorflow/blob/master/tensorflow/compiler/xla/service/hlo_memory_scheduler.cc#L484

// NOTE(dimvar): this is quite ugly and should be changed. It's unclear
// why we care about transitive sizes; when scheduling a node, its input
// and output buffers should be all that matters, not its "history".

My confusion is the same as dimvar noted in the code:

Why is extra_users and total_sizes accumulated? "why we care about transitive sizes"?

For each node(hlo_instruction), when look at extra_users of that node, it indicates there were this many branches before we visit current node.

why is "extra_users" used as the major parameter for DFS memory scheduler?

Thanks a lot for your time

Kevin

[Sanjoy Das]

+Dimitris Vardoulakis 

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[dim...@google.com]

Hi Kevin,

The DFS scheduler needs a heuristic to select among the children of a node to continue the search. I don't know why "transitive sizes" is used. I'm guessing someone tried it back in the day, and found that it worked well enough for the programs that they tried. I doubt there is a deep reason. I don't have any new knowledge since I added this comment, because I haven't worked on this pass since then.

[t kevin]

hi Dimitris ,Sanjoy,

Thanks for the reply.
Indeed this "mysterious" implementation works very well.

Kevin

'dim...@google.com' via XLA development <xla...@googlegroups.com>
于2022年1月6日周四 02:52写道：

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