Skip known bad vertices in power recovery #5150
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clang-tidy review says "All clean, LGTM! 👍" |
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Results for other cores (all on Ibex
BlackParrot
Ariane
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bad_vertices_ needs to be cleared at the end of recoverPower so it doesn't persist between calls. |
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Ready for review? |
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Sure |
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I tested the current recover power designs and they look fine. It just need the clear mentioned above to be ready to merge. |
Signed-off-by: Krzysztof Bieganski <[email protected]>
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Added the clear. |
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clang-tidy review says "All clean, LGTM! 👍" |
maliberty
reviewed
May 24, 2024
Signed-off-by: Krzysztof Bieganski <[email protected]>
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clang-tidy review says "All clean, LGTM! 👍" |
maliberty
approved these changes
May 28, 2024
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In power recovery, vertices that have already been tried and rejected can be tried again if they happen to be on another path we look at. Usually, the result is the same – we reject the vertex. Not only is this work unnecessary, it also prevents us from trying another (possibly better) vertex later in the path. Some stats on vertices that are tried in #4982:
max_length492/Yload_slew487/Yload_slew465/Yload_slew447/Yload_slew409/Yload_slew400/Yload_slew375/Yload_slew57/Yload_slew407/Yfdct_zigzag.dct_mod.dct_block_0.dct_unit_0.ddin\[7\]$_DFFE_PN0P_/QNmax_length63/Y_085272_/Yload_slew402/Y_083048_/Ywire301/Yload_slew62/Yload_slew446/Y_078958_/Yload_slew399/Yload_slew486/Yload_slew462/Yload_slew461/Y_118922_/Y_122581_/CONload_slew177/YIn the worst case, one vertex is visited 1325 times, 1324 of which result in worse worst slack. That's also about a quarter of all attempts.
This patch makes it so we don't revisit the vertices that were already rejected.
In the example in #4982, this speeds up GRT from ~1.5h to around 6 minutes, so we're looking at ~15x the performance on that particular design.
Also, the actual power recovery seems overall more effective (not sure how to weigh these values against each other).
