CDT and Parallella

Multicore Debugging for the Masses

Andreas Olofsson (Adapteva)

Marc Khouzam (Ericsson)

About us

• Andreas Olofsson
• Founder and CEO of Adapteva
• Creator of Parallella


• Marc Khouzam
• CDT Committer, lead for Debug
• Working on Multicore Debugging since the fall of 2010

Agenda

• Parallella and Epiphany
• Debugging Parallella with CDT
• Possible next steps
• Other news for CDT Debug
• Q&A

An Epiphany Introduction

Massive Parallelism Has Arrived!

• How in the ^**&#@ are we doing to program AND DEBUG this??

The Parallella Computer

Debugging for Massive Parallelism

Debugging Parallella with CDT

• Ericsson (CDT) and Adapteva (Parallella) collaboration
• Goals:
• Open-source multicore debug solution for Parallella
• Open example for multicore debug in CDT
• Easy access to multicore debugging for all
• Collaboration and exposure to improve multicore debug

Previous Debug Solution for Epiphany

• Single-core traditional hardware debug using GDB
• Load program on a core and debug it
• No global perspective
• Needs one session per core to deal with entire system
• Does not scale past 16 cores, and even then

Implemented Enhancements

• Single session to debug the entire Epiphany
• Connecting to an already running system


• A debug thread is a single core
• A debug process is a group of cores running the same binary
• Traditional debugging for each core


• Epiphany Multicore Visualizer


• Support for Non-stop mode

Debugging the main chip

• Remote Debug of ARM chip (Ubuntu) with GDB/gdbserver
• Traditional debug operations for ARM program

Multicore Debugging the Epiphany

• Remote Multicore Debug of Epiphany with e-GDB/e-server
• Traditional debug operations for all Epiphany cores

Multicore Debugging Parallella

• Debug using both sessions

Scaling issues

• Debug view with 64 cores
• Unmanageable!
• Need Visualization

Generic Multicore Visualizer

• Monitor entire system at a glance
• Control program execution from Visualizer
• Synchronized with Debug view

Epiphany Multicore Visualizer

• Hardware layout
• Cores and network
• Process distribution
• Load of cores
• Load of network

Epiphany Multicore Visualizer Layout

• Actual hardware layout
• Core IDs
• Color shows binary loaded
• Selection of cores
• Status bar info

Program Distribution and Load

• Layout with network
• Load per core
• Load per network link

64-core Layout

64-core Load

Possible next steps

Status reporting

• Running state per core in Visualizer

Grouping

• GDB IT sets support
• Run Control operations on group
• Breakpoints limited to group

User-selectable cores to debug

• Attach to a group/process to debug it
• Debug view only shows attached groups
• Attaching directly from Visualizer

Debugging thousands of cores

• 4096 cores

Debugging thousands of cores

Possible solutions

• Zooming
• Use of scrollbars or mouse drag
• Use of colors to pin-point an issue
• Automatic issue detection


• More study needed, more collaboration

Visualizer Zooming

• Zoom directly
• Pin & Clone
• Multiple Visualizer views
• One high-level view
• One or more zoomed views

Visualizer Pin & Clone

• The entire Parallella: ARM and Epiphany chips

Other news for CDT Debug

Return Values

• After a Step-Return
• Top element of Variables view
• Removed at next execution
• Plan to generalize for Step-Over

Trace Control View

• Graphical view
• Navigation Scrollbar
• Circular Buffer
• Disconnected Tracing
• Optional automatic refresh

Dynamic-Printf

• No re-compiling
• No re-deploying
• Debugger can disconnect

Hardware and Temporary Breakpoints

• Through Add Breakpoint or Breakpoint Properties

New Launch UI

Standalone CDT Debugger

> run-gdbstandalone.sh [-b <build_log>] -e <binary> [arg1 ... argn]

Resources

Parallella
Multicore Debug Workgroup
CDT 8.3 Debug New & Noteworthy
CDT 8.4 Debug New & Noteworthy
CDT Debug FAQ
CDT Standalone Debugger
Adapteva
Ericsson Open-Source

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