design automation conference (dac), june 6 th, 20131 taming the complexity of coordinated place and...

Design Automation Conference (DAC), June 6th, 2013 1

Taming the Complexity of Coordinated Place and Route

Jin Hu†, Myung-Chul Kim†† and Igor L. Markov†††

†Systems and Technology Group (STG), IBM, Fishkill, NY ††Systems and Technology Group (STG), IBM, Austin, TX

†††Dept. of Computer Science and Engineering (CSE), University of Michigan

[speaker]


Placement Solutions Must Be Routable

DAC 1998

DAC 2000 (Capo)

Back to the Future ? Things have changed:

Much larger, more challenging P&R instancesStronger, faster baseline placers & routersVery precise evaluation of results through contestsRecent trend: simultaneous P&R

Our contributions to P&R:1. Speed2. Speed3. Speed


1st place at ICCAD`12

What DAC`13 Reviewers Thought of Our Contributions


The Need for Speed Congestion estimation during global

placement requires fast routingWe can do 75K nets/sec (1 thread)Our competition – 6K nets/sec (1 thread)Our router is called 20 times during GP

and still takes <15% of total runtime The secret – simplify the router’s task Additional secrets

Scrap Dijkstra and A*-searchUse array-based, cache-friendly algorithms


How to Avoid Extra Work The placer invokes a router The router works hard to reduce violations The placer changes locations The placer invokes a router The router works hard to reduce violations The placer changes locations The placer invokes a router The router works hard to reduce violations

…


How to Avoid Extra Work

Spread the router’s work across global-placement iterationsDo not solve routing every time – no need to! Reuse work


Incremental Global Routing When movable objects stay in same GCells,

reuse routes When objects move a little, reuse routes When relative positions do not change,

reuse routes

When everything changes, try to reuse routes


Incremental Maze Routing ? Dijkstra and A*-search don’t do incremental ! They are also slow – pointer-chasing

in binary heaps is no good for cache

Need something else !


The Answer – Bellman-Ford (BF) Bellman-Ford can be incremental Bellman-Ford uses no pointers Bellman-Ford is cache-friendly Worst-case complexity is O(V 2)

versus O(V log V) for Dijkstra and A*-search So, many skeptics:

The trick: run 1 pass of BF at a time, incrementally


More on Bellman-Ford in Our Paper Finishes sooner with alternating passes (known) Generalizes monotonic routing (obvious) Finds some non-monotonic routes in one pass

(with our improvements) Theorem 1: optimal routes with k monotonic

segments are found in k passesFor most nets, k is very small


What About Scenic Routes?

Router invocations mark routing congestion The placer spreads cells to eliminate congestion Do not waste time on scenic routes

(but incremental Bellman-Ford can find them anyway)



Congestion map vs. Estimate (Early GP)

LIRE1 Iteration of BFG-R



LZ Routing1 Iteration of BFG-R



L Routing1 Iteration of BFG-R


Congestion map vs. Estimate (Mid GP)

1 Iteration of BFG-R LIRE



1 Iteration of BFG-R LZ Routing


Congestion map vs. Estimate (Late GP)

1 Iteration of BFG-R LIRE



1 Iteration of BFG-R LZ Routing

Congestion Classification: Cell-based congestion: cell-to-cell proximity

Solution: cell bloating (known)

Layout-based congestion: due to static design properties (blockages, routing obstacles)Solution: static whitespace injection

Remotely-induced layout-based congestion: caused by non-local factors, e.g., long netsSolution: tricky



Packing Peanut vs. Macro Expansion

After 4 invocations of placement

Initial Macro

After 2 invocations of placement

Packing peanut

Facilitates full use of available resources --- does not overconstrain placement


Example During Global Placement

Congestion Map Placement


Empirical ValidationCompares against official results from ICCAD 2012 Contest[Viswanathan et al. – ICCAD 2012]

CoPR implemented using C++ (g++ 4.7.0) using OpenMP

CoPR is 1% slower than SimPLR, which was 5.7x faster than RippleCoPR has 2% and 7% better quality than SimPLR and NTUplace [no runtime factor]

CoPR invokes LIRE once every 3 placement iterations, contributing 14.3% of total runtime

Conclusions Crazy fast coordinated place-and-route

Through incremental routing and better algorithms Three congestion types

+ ways to relieve them in global placement


Placement Routing

1st place at ICCAD`12


Backup: Placements Visualized


Backup: Detailed Placement

Congestion Aware DPAfter Global Placement Congestion UNaware DP

design automation conference (dac), june 6 th, 20131 taming the complexity of coordinated place and...

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