Dynamic node fails with routing congestion

[gadfort]

Describe the bug

Between 4b729ea...6e29df0 something changed that is causing a routing congestion issue on a previously working design.
It appears that the change that broke this was after 588bc37

Expected Behavior

No routing congestion issue

Environment

OpenROAD v2.0-22186-g6e29df0746 
Features included (+) or not (-): +GPU +GUI +Python
This program is licensed under the BSD-3 license. See the LICENSE file for details.
Components of this program may be licensed under more restrictive licenses which must be honored.

To Reproduce

sc_issue_dynamic_node_job0_skywater130_sky130hd_route.global0_20250615-011417.tar.gz

tar xvf sc_issue_dynamic_node_job0_skywater130_sky130hd_route.global0_20250615-011417.tar.gz
cd sc_issue_dynamic_node_job0_skywater130_sky130hd_route.global0_20250615-011417
./run.sh

Relevant log output

[INFO GRT-0101] Running extra iterations to remove overflow.
[INFO GRT-0103] Extra Run for hard benchmark.
[WARNING GRT-0230] Congestion iterations cannot increase overflow, reached the maximum number of times the total overflow can be increased.
[INFO GRT-0197] Via related to pin nodes: 52735
[INFO GRT-0198] Via related Steiner nodes: 2330
[INFO GRT-0199] Via filling finished.
[INFO GRT-0111] Final number of vias: 95509
[INFO GRT-0112] Final usage 3D: 393857

[INFO GRT-0096] Final congestion report:
Layer         Resource        Demand        Usage (%)    Max H / Max V / Total Overflow
---------------------------------------------------------------------------------------
li1                  0             0            0.00%             0 /  0 /  0
met1             30211         25809           85.43%             4 /  1 / 799
met2             38127         36714           96.29%             0 / 10 / 3532
met3             32346         27842           86.08%             4 /  1 / 826
met4             14910         12881           86.39%             0 /  5 / 1358
met5              5112          4084           79.89%             2 /  0 / 140
---------------------------------------------------------------------------------------
Total           120706        107330           88.92%            10 / 17 / 6655

[INFO GRT-0018] Total wirelength: 1045488 um
[INFO GRT-0014] Routed nets: 7246
[ERROR GRT-0116] Global routing finished with congestion. Check the congestion regions in the DRC Viewer.
[ERROR FLW-0001] Global routing failed, saving database to reports/dynamic_node_top_wrap.globalroute-error.odb
Error: sc_global_route.tcl, 64 FLW-0001

Screenshots

No response

Additional Context

No response

[maliberty]

@gadfort sometimes grt is the symptom rather than the cause. Does anything differ substantially in the good/bad results pre-grt? grt itself hasn't had a lot of big changes recently.

[maliberty]

Would you include a working run as well for comparison?

[gadfort]

@maliberty there are a whole host of instances named "placeXX" which I haven't noticed before (they seem to come from this PR #7485). I will upload a working run in a little while.

[gadfort]

Here is a working one from 588bc37: https://drive.google.com/file/d/1cSI4y8LkhVK1xZUtJABpgQRvhxv9pwo4/view?usp=sharing

[maliberty]

@povik #7485 is your PR so please investigate. I've started a quick look as well.

[povik]

@gadfort where can I find a gpl log for the failing run?

[gadfort]

Log from failing build:
place.global.log

Log from working build:
place.global.log

[povik]

Thanks Peter

The first RD in the failing run spikes up the target density:

[INFO GPL-0063] New Target Density:             0.9584

vs

[INFO GPL-0063] New Target Density:             0.6136

on the passing run.

Final densities (after all TD/RD) are 0.84 vs 0.69.

The cell areas after gpl are similar (old):

Design area 106462 u^2 44% utilization.
Cell type report:                       Count       Area
  Tap cell                               3202    4006.34
  Timing Repair Buffer                    284    4762.07
  Inverter                                151     844.56
  Sequential cell                        2257   65683.00
  Multi-Input combinational cell         3303   35172.48
  Total                                  9197  110468.45

and (new)

Design area 107538 u^2 44% utilization.
Cell type report:                       Count       Area
  Tap cell                               3202    4006.34
  Timing Repair Buffer                    951    4827.13
  Inverter                                151     854.57
  Sequential cell                        2257   65683.00
  Multi-Input combinational cell         3303   36173.44
  Total                                  9864  111544.48

[gadfort]

sc_issue_dynamic_node_job0_skywater130_sky130hd_place.global0_20250616-083250.tar.gz

@povik FYI

[maliberty]

The seems like a very large jump in density. Perhaps @gudeh work to do filler decreasing instead would help. I am curious why the density jumps so much in one run vs the other when the final area is so similar.

[gudeh]

Log from failing build: place.global.log

Log from working build: place.global.log

On the failing log I noticed this warning on the second timing-driven gpl iteration: [WARNING RSZ-2005] cannot find a viable buffering solution on pin _5181_/Y after 1 rounds of buffering (no solution meets design rules).

On the working log we have 13 routability iterations with around 1% area inflation each, which is ok. While the failing log we have a 76% increase in area already on the first routability iteration, coming from a really high routing congestion. I will investigate further

[povik]

On the failing log I noticed this warning on the second timing-driven gpl iteration: [WARNING RSZ-2005] cannot find a viable buffering solution on pin 5181/Y after 1 rounds of buffering (no solution meets design rules).

That's worth looking at but it's probably not related to the excessive inflation or the congestion.

[gudeh]

sc_issue_dynamic_node_job0_skywater130_sky130hd_place.global0_20250616-083250.tar.gz

@povik FYI

@gadfort I am getting this error with such tarball:

[ERROR ODB-0477] dbTable mask/shift mismatch 127/7 vs 4095/12
[ERROR GUI-0070] ODB-0477