Refactor LXU cache logic in TBE fwd training #1295
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This pull request was exported from Phabricator. Differential Revision: D39353035 |
Summary: Pull Request resolved: pytorch#1295 The LXU cache logic is in the critical path of the forward TBE kernel. Even when the LXU cache is not used, the kernel still checks whether a row should be fetched from the cache or HBM at runtime. The branching logic should be harmless for the memory (subsystem) bound case. However, it could add significant overhead if TBE is conditional bound. (We have observed that FP16 weight type is generally compute or conditional bound, while FP32 weight type is memory bound.) This diff adds a static conditional in the forward TBE kernel to enable/disable the LXU cache code path at compile time. At runtime, the host selects the kernel with/without cache enabled based on whether the LXU cache is present. This diff also moves the conditional outside the D loop. It should add a small benefit for the large D cases when cache is used. Reviewed By: jspark1105 Differential Revision: D39353035 fbshipit-source-id: bfd3d842971091e954e49c6c8fad034db1fcbc9b
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This pull request was exported from Phabricator. Differential Revision: D39353035 |
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Summary:
The LXU cache logic is in the critical path of the forward TBE kernel.
Even when the LXU cache is not used, the kernel still checks whether a
row should be fetched from the cache or HBM at runtime. The branching
logic should be harmless for the memory (subsystem) bound case.
However, it could add significant overhead if TBE is conditional
bound. (We have observed that FP16 weight type is generally compute
or conditional bound, while FP32 weight type is memory bound.)
This diff adds a static conditional in the forward TBE kernel to
enable/disable the LXU cache code path at compile time. At runtime,
the host selects the kernel with/without cache enabled based on
whether the LXU cache is present.
This diff also moves the conditional outside the D loop. It should
add a small benefit for the large D cases when cache is used.
Differential Revision: D39353035