Add extended lookahead map #1449

acomodi · 2020-07-23T14:01:29Z

Description

This PR adds a new lookahead map method called extended map. This new kind of lookahead takes the same mechanisms of generation of the cost map as found in the connection box based lookahead currently implemented in the SymbiFlow/VTR fork, and uses the OPIN -> CHAN and CHAN -> IPIN delay information from the upstream lookahead map.

This PR includes new code to perform the node sampling which is more robust with respect to the current implementation, but takes more time to compute, hence the need of parallelize the graph exploration to fill the map costs.

Even with parallelization, though, the lookahead generation takes too long for the current regression tests in VTR, therefore the choice of adding a completely new lookahead type (extended map), so not to interfere with the current implementation.

Related Issue

There is no issue currently open, but this PR is one of the last ones needed to fully upstream the SymbiFlow/VTR fork's changes needed to perform P&R using upstream VTR for 7-series devices.

Motivation and Context

The current lookahead map implementation is not sufficient to provide accurate estimates during the router expansions for 7-Series devices. This results in high run-times with bad CPD results. To achieve better results, the lookahead build strategy needed to be improved (at least for 7-series).

How Has This Been Tested?

The new lookahead has been tested on SymbiFlow architectures: the issue keeping track of the progress is this one

Types of changes

Bug fix (change which fixes an issue)
New feature (change which adds functionality)
Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

My change requires a change to the documentation
I have updated the documentation accordingly
I have added tests to cover my changes
All new and existing tests passed

vaughnbetz · 2020-07-30T17:24:01Z

Not sure what all the failures are due to -- rerun?

vaughnbetz · 2020-07-30T17:40:58Z

Looks like at least some of these failures are due to failures in the new lookahead builder.

acomodi · 2020-08-04T15:22:32Z

I have restored the changes to only add the extended lookahead map. Turns out that, even with the bugfix of the CHANX/CHANY that got merged together, CPD and in general QoR seems to be worsening also for the strong regression tests.

The problem is that the lookahead map and the extended lookahead map use two very different methods of both generating and querying the cost map.

I am unsure whether the two methods can be merged together safely and preserve the QoR of vtr regression tests, as well as run-time.

acomodi · 2020-08-11T08:49:28Z

I believe this is ready for review at the current state.

I have exported some of the code from the lookahead map in the lookahead_map_utils file as it could be shared with the extended map code.

This implementation does not interfere with the regression tests as they all use the map lookahead.
I might as well add some tests which do make use of the extended map to test its behaviour and avoid regressions as well.

acomodi · 2020-08-11T15:08:11Z

@vaughnbetz @litghost @HackerFoo FYI, I think this PR is ready for a first review iteration

vpr/src/route/route_timing.cpp

litghost

LGTM

- New sampling method for lookahead map. - New spiral hole filling algorithm - Use a lightweight version of PQ_Entry (PQ_Entry_Lite) - Use maps in run_dijkstra() - Move context of router_lookahead_map_utils inside of util namespace. - Parallelization of lookahead generation lookahead: add new extended map lookahead This lookahead generates a map with a more complex and complete way of sampling and expanding the nodes to reach all destinations. The dijkstra expansion is parallelized to overcome the higher number of samples needed. It also adds a penalty cost factor based on distance between the origin and destination nodes. extended_lookahead: cleaned code and reduced code duplication Signed-off-by: Dusty DeWeese <[email protected]> Signed-off-by: Keith Rothman <[email protected]> Signed-off-by: Alessandro Comodi <[email protected]>

Signed-off-by: Alessandro Comodi <[email protected]>

- The cost map filling routine has been simplified and the relevant code extracted in two different sub-routines (penalty calculation, cost filling) - Commented used Doxygen compatible style some of the important methods and class members Signed-off-by: Alessandro Comodi <[email protected]>

Signed-off-by: Alessandro Comodi <[email protected]>

- Added better description on the user options - Added test with random_shuffle nodes reordering Signed-off-by: Alessandro Comodi <[email protected]>

Signed-off-by: Alessandro Comodi <[email protected]>

acomodi · 2020-09-11T10:48:44Z

@vaughnbetz I have rebased and solved all the conflicts due to the RCV merge

vaughnbetz · 2020-09-11T16:44:29Z

Thanks @acomodi . There are a few unresolved conversations, requests.

Can you go through and comment on them: either change (mostly commenting and changing to RRNodeIDs) or make a new PR/issue to track those updates so we don't lose them?
Waiting for kokoro to finish.

@acomodi : if you can do 1 (comment / transfer to new PR or issue) while we're waiting for 2 (kokoro) then I can merge once kokoro finishes.

acomodi · 2020-09-11T17:06:04Z

@vaughnbetz Ok, I will open a new PR based on this one to add the additional comments and the assertion, as well as opening the issues.

I do not have time unfortunately to update the RRNodeId today, but I can open an issue about it as well

acomodi · 2020-09-11T17:18:51Z

Opened issues:

vaughnbetz · 2020-09-11T21:40:19Z

Thanks @acomodi. This is a major PR !
Tracking the remaining nits / cleanups with other issues sounds good.
Merged.

probot-autolabeler bot added build Build system lang-cpp C/C++ code lang-make CMake/Make code VPR VPR FPGA Placement & Routing Tool labels Jul 23, 2020

acomodi mentioned this pull request Jul 23, 2020

New Lookahead map status SymbiFlow/vtr-verilog-to-routing#517

Open

acomodi requested review from vaughnbetz, litghost and HackerFoo and removed request for HackerFoo July 23, 2020 14:09

probot-autolabeler bot added the libarchfpga Library for handling FPGA Architecture descriptions label Jul 27, 2020

acomodi force-pushed the add-extended-lookahead-map branch from 6586087 to 88b5632 Compare July 27, 2020 19:46

probot-autolabeler bot added the tests label Jul 27, 2020

acomodi changed the title ~~Add extended lookahead map~~ WIP: Add extended lookahead map Jul 27, 2020

acomodi force-pushed the add-extended-lookahead-map branch from 88b5632 to 9baa569 Compare August 4, 2020 13:51

This was referenced Aug 4, 2020

WIP: New Lookahead sampling method #1367

Closed

WIP: Enhancing VPR lookahead map #1351

Closed

acomodi force-pushed the add-extended-lookahead-map branch from c313c39 to 60b3b25 Compare August 10, 2020 12:35

acomodi changed the title ~~WIP: Add extended lookahead map~~ Add extended lookahead map Aug 10, 2020

acomodi force-pushed the add-extended-lookahead-map branch from 60b3b25 to f4105e2 Compare August 10, 2020 15:34

probot-autolabeler bot added the VTR Flow VTR Design Flow (scripts/benchmarks/architectures) label Aug 11, 2020

acomodi force-pushed the add-extended-lookahead-map branch from bdd96dd to 15c54dd Compare August 11, 2020 14:25

litghost reviewed Aug 11, 2020

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vpr/src/route/route_timing.cpp Outdated Show resolved Hide resolved

litghost approved these changes Aug 11, 2020

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acomodi force-pushed the add-extended-lookahead-map branch from 266a8ce to fe3cad5 Compare August 18, 2020 16:26

acomodi force-pushed the add-extended-lookahead-map branch 2 times, most recently from a8e9b8c to 53bfad8 Compare September 10, 2020 17:22

acomodi added 18 commits September 11, 2020 11:22

tests: added extended_map to router_lookahead strong test

99d3b94

Signed-off-by: Alessandro Comodi <[email protected]>

context: removed not needed segment_inf member from the device ctx

53f2dd1

Signed-off-by: Alessandro Comodi <[email protected]>

extended_lookahead: fix SRC/OPIN delay

894ec9f

Signed-off-by: Alessandro Comodi <[email protected]>

extended_map: added in-code comments

2472366

Signed-off-by: Alessandro Comodi <[email protected]>

lookahead_map_utils: added comments

c254627

Signed-off-by: Alessandro Comodi <[email protected]>

lookahead: wider usage of RRNodeId where possible

b3e6f83

Signed-off-by: Alessandro Comodi <[email protected]>

run make format

98e56f8

Signed-off-by: Alessandro Comodi <[email protected]>

lookahead_cost: avoid building the segment map

d9d1ed8

Signed-off-by: Alessandro Comodi <[email protected]>

address review comments

aefe2f1

- Added better description on the user options - Added test with random_shuffle nodes reordering Signed-off-by: Alessandro Comodi <[email protected]>

lookahead_sampling: simplified find_sample_regions code

39a5524

Signed-off-by: Alessandro Comodi <[email protected]>

reg_test: added missing golden results

392996a

Signed-off-by: Alessandro Comodi <[email protected]>

extended_lookahead: re-enable SRC/OPIN lookahead cost

070bb74

Signed-off-by: Alessandro Comodi <[email protected]>

lookahead: addressed review comments

98cc4d8

Signed-off-by: Alessandro Comodi <[email protected]>

lookahead: added comment to the special segment type constant index

f4b7155

Signed-off-by: Alessandro Comodi <[email protected]>

route_timing: remove un-necessary headers

fb214f2

Signed-off-by: Alessandro Comodi <[email protected]>

lookahead: fixed rebase conflicts

3111500

Signed-off-by: Alessandro Comodi <[email protected]>

acomodi force-pushed the add-extended-lookahead-map branch from 53bfad8 to 3111500 Compare September 11, 2020 10:16

acomodi requested a review from vaughnbetz September 11, 2020 10:48

This was referenced Sep 11, 2020

Add extended lookahead map followup #1536

Merged

Revisit the median cost entry calculation for the lookahead #1537

Open

vaughnbetz merged commit 95843c2 into verilog-to-routing:master Sep 11, 2020

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Add extended lookahead map #1449

Add extended lookahead map #1449

acomodi commented Jul 23, 2020

vaughnbetz commented Jul 30, 2020

vaughnbetz commented Jul 30, 2020

acomodi commented Aug 4, 2020

acomodi commented Aug 11, 2020

acomodi commented Aug 11, 2020

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acomodi commented Sep 11, 2020

vaughnbetz commented Sep 11, 2020 •

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acomodi commented Sep 11, 2020

acomodi commented Sep 11, 2020

vaughnbetz commented Sep 11, 2020

Add extended lookahead map #1449

Add extended lookahead map #1449

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acomodi commented Jul 23, 2020

Description

Related Issue

Motivation and Context

How Has This Been Tested?

Types of changes

Checklist:

vaughnbetz commented Jul 30, 2020

vaughnbetz commented Jul 30, 2020

acomodi commented Aug 4, 2020

acomodi commented Aug 11, 2020

acomodi commented Aug 11, 2020

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acomodi commented Sep 11, 2020

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acomodi commented Sep 11, 2020

vaughnbetz commented Sep 11, 2020

vaughnbetz commented Sep 11, 2020 •

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