# Presentation: 718779

## Fault Tolerance and Adaptation in Large Scale, Heterogeneous, Soft Real-Time Systems

- RTES Collaboration

- (NSF ITR grant ACI-0121658)

- Paul Sheldon
- Vanderbilt University

## Introduction

- The Problem
- Goals and Deliverables
- Demonstration system
- Comments

- CMS Week

- 16 March 2005

## A 20 TeraHz Real-Time System:BTeV Trigger... some similarities to CMS

**A 20 TeraHz Real-Time System**:BTeV Trigger... some similarities to CMS

- Input: 800 GB/s (2.5 MHz)
- Level 1
- Lvl1 processing: 190s
- rate of 396 ns
- 528 “8 GHz” G5 CPUs
- (factor of 50 event reduction)
- high performance interconnects
- Level 2/3:
- Lvl 2 processing: 5 ms
- (factor of 10 event reduction)
- Lvl 3 processing: 135 ms
- (factor of 2 event reduction)
- 1536 “12 GHz” CPUs commodity networking
- Output: 200 MB/s (4 kHz) = 1-2 Petabytes/year

- CMS Week

- 16 March 2005

## The Problem:  Early Project Review

- “Given the very complex nature of this system  where thousands of events are simultaneously and asynchronously cooking, issues of data integrity, robustness, and monitoring are critically important and have the capacity to cripple a design if not dealt with at the outset...”    “BTeV [needs to] supply the necessary  level  of “self-awareness” in the trigger system.”
- [June 2000 Project Review]

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**Notes:**
Complexity of the event and noise, missing channels, aliasing, etc.

## Chap. 9 & Appendix E, DAQ/HLT TDR

- ...**demonstrate that** the current system and its associated protocols are such that **all transient faults are handled in real-time and that, after relatively short periods of time, the system resumes its correct operation****.**
- The implementation of the established fault-tolerant protocols is tested by using prototype software and hardware developed in the context of the CMS-DAQ R&D. **This the step where fault-injection tests are carried out.**
- [Fault Injection]  is particularly important because fault-handling code is exercised only when a fault occurs. Given that the occurrence of faults should be the exception, rather than the rule, such code is therefore either not tested, or is only minimally tested. To establish the correctness and scaling of the fault handling mechanisms in the design, **fault injection at the level of the prototype Event Builder and in a simulation of the full CMS system is used to establish the correctness of the actual implementation**.

- CMS Week

- 16 March 2005

## For lack of a better name:  RTES

- The Real Time Embedded Systems Group
- A collaboration of five institutions:
- University of Illinois
- University of Pittsburgh
- University of Syracuse
- Vanderbilt University (PI)
- Fermilab
- NSF ITR grant ACI-0121658
- Funds Computer Scientists/Electrical Engineers with expertise in:
- High performance, real-time system software and hardware,
- Reliability and fault tolerance,
- System specification, generation, and modeling tools.

- RTES Graduate Students

- CMS Week

- 16 March 2005

**Notes:**
Including both studies of fault management and producing software

## RTES Goals

- High availability
- Fault handling infrastructure capable of
- Accurately identifying problems (where, what, and why)
- Compensating for problems (shift the load, changing thresholds)
- Automated recovery procedures (restart / reconfiguration)
- Accurate accounting
- Extensibility (capturing new detection/recovery procedures)
- Policy driven monitoring and control
- Dynamic reconfiguration
- adjust to potentially changing resources

- CMS Week

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**Notes:**
Available despite failures
Have a “pluggable” nature
dynamic nature
Easy configuration and interfacing to control components like an alarm tool

## RTES Goals (continued)

- Faults must be detected/corrected ASAP
- semi-autonomously
- with as little  human intervention as possible
**distributed & hierarchical monitoring and control**
- Life-cycle maintainability and evolvability
- to deal with new algorithms, new hardware and new versions of the OS

- CMS Week

- 16 March 2005

**Notes:**
Available despite failures
Have a “pluggable” nature
dynamic nature
Easy configuration and interfacing to control components like an alarm tool

## The RTES Solution

**Analysis**

**Runtime **

**Configuration, Design and**
**Analysis**

- Algorithms

**Fault ****Behavior**

**Resource**

**Synthesis**

**Performance**
**Diagnosability**
**Reliability**

**Experiment****Control**
**Interface**

**Synthesis**

**Feedback**

**Modeling**

**Reconfigure **

**Region ****Operations Mgr**

**L2,3/CISC/RISC**

**L1/DSP**

** ****Soft                    Real Time                         Hard**

- CMS Week

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## RTES Deliverables

- A hierarchical fault management system and toolkit:
- Model Integrated Computing  [Vanderbilt]
- GME (Generic Modeling Environment) system modeling tools
- and application specific “graphic languages” for modeling system configuration, messaging, fault behaviors, user interface, etc.
- ARMORs (Adaptive, Reconfigurable, and Mobile Objects for Reliability)  [Illinois]
- Robust framework for detection and reaction to faults in processes
- VLAs (Very Lightweight Agents for limited resource environments)  [Syracuse and Pittsburgh]
- To monitor/mitigate at every level
- DSP, Supervisory nodes, Linux farm, etc.

- CMS Week

- 16 March 2005

## GME: Configuration through Modeling

- Multi-aspect tool, separate views of
- Hardware – components and physical connectivity
- Executables – configuration and logical connectivity
- Fault handling behavior using hierarchical state machines
- Model interpreters can generate the system image
- At the code fragment level (for fault handling)
- Download scripts and configuration
- Modeling “languages” are application specific
- Shapes, properties, associations, constraints
- Appropriate to application/context
- System model
- Messaging
- Fault mitigation
- GUI, etc.

- CMS Week

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**Notes:**
Dataflow between executables or modules aspect
Code generation depends on the complexity of the model interpreter
Tool set from VU
Systems modeling

## Modeling Environment

- CMS Week

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## ARMOR

**A**daptive **R**econfigurable **M**obile **O**bjects of **R**eliability:
- Multithreaded processes composed of replaceable building blocks
- Provide error detection and recovery services to user applications
- Hierarchy of ARMOR processes form runtime environment:
- System management, error detection, and error recovery services distributed across ARMOR processes.
- ARMOR Runtime environment is itself self checking.
- 3-tiered ARMOR support of user application
- Completely transparent and external support
- Enhancement of standard libraries
- Instrumentation with ARMOR API

- CMS Week

- 16 March 2005

## ARMOR Scaleable Design

- ARMOR processes designed to be *reconfigurable*:
- Internal architecture structured around event-driven modules called *elements*.
- Elements provide functionality of the runtime environment, error-detection capabilities, and recovery policies.
- Deployed ARMOR processes contain only elements necessary for required error detection and recovery services.
- ARMOR processes *resilient* to errors by leveraging multiple detection and recovery mechanisms:
- Internal self-checking mechanisms to prevent failures from occurring and to limit error propagation.
- State protected through checkpointing.
- Detection and recovery of errors.
- ARMOR runtime environment *fault-tolerant* and *scalable*:
- 1-node, 2-node, and *N*-node configurations.

- CMS Week

- 16 March 2005

## Execution ARMOR in Worker

- Worker

- Exec ARMOR

- Filter 1

- Filter 2

- Event Builder

**ARMOR Microkernel**

**Msg table**

**Named pipe**

**Msg routing**

**Process mgmt**

**App id mgmt**

**Crash detection**

- Infrastructure elements

**Elvin/Armor msg converter**

**Hang detection**

**Node status report**

**Filter crash report**

**Bad data report**

**Execution time report**

- Custom elements

**Memory leak report**

- CMS Week

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## Very Lightweight Agents

- Minimal footprint
- Platform independence
- Employable everywhere in the system!
- Monitors hardware and software
- Handles fault detection& communications with higher level entities

- CMS Week

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## Demonstration System

- Demonstrate fault mitigation and recovery in a “large” cluster (64 node)
- 54 worker nodes (108 CPUs) divided into 9 “regions”
- 9 regional managers
- 1 Global manager
- Distributed and hierarchical monitoring and error handling
***Inject errors and watch for appropriate behavior***

- CMS Week

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## The Demonstration System Architecture

- public

- private

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## Prototype Trigger Farms at Fermilab

- CMS Week

- 16 March 2005

## L2/3 Prototype Farm Components

- Using PC’s from old PC Farms at Fermilab
- 3 dual-CPU Manager PCs
- boulder (1 GHz P3) - meant for data server
- iron (2.8 GHz P4) - httpd, BB and Ganglia gmetad
- slate (500 MHz P3) - httpd, BB
- Managers have a private network through 1 Gbps link
- bouldert, iront, slatet
- 15 dual-CPU (500 MHz P3) workers (btrigw2xx)
- 84 dual-CPU (1GHz P3) PC workers (btrigw1xx)
- No plans to add more, but may replace with faster ones
- Ideal for RTES
- 11 workers already have problems!
- A Heterogeneous Mix of Aging Systems!

- CMS Week

- 16 March 2005

## Errors Types

- “Bad event” corrupt event data detected by filter application, message sent for logging/counting
- Kill a filter application
- ARMOR detects its absence restarts it
- Hang a filter application
- Time-out message from event source triggers killing
- Filter restarted by its ARMOR
- Exponential slowing of filter
- Detected by VLA, notifies ARMOR, kills filter application
- ARMOR restarts filter app

- CMS Week

- 16 March 2005

## ...Errors Types

- Increase in memory usage (memory leak)
- Detected by VLA, notifies ARMOR, kills filter application
- ARMOR restarts filter app
- Regional growth in filter execution time (all or many filter processes slow)
- Regional ARMOR takes corrective action: increases threshholds in filter

- CMS Week

- 16 March 2005

## Near term goals

- Run 65 node demo 24/6/365
- Use to debug/shake down tools (ARMORs, VLAs, modeling)
- Improve/update
- Use as a running experiment!
- Measure/characterize performance of tools
- Improve monitoring interface:  system info provided to human operator
- More realistic faults, and more complete set
- Filter feedback

- CMS Week

- 16 March 2005

## Comments

- This is an integrated approach – from hardware to physics applications
- Standardization of resource monitoring, management, error reporting, and integration of recovery procedures can make operating the system more efficient and make it possible to comprehend and extend.
- There are real-time constraints that must be met
- Scheduling and deadlines
- Numerous detection and recovery actions
- The product of this research will
- Automatically handle simple problems that occur frequently
- Be as smart as the detection/recovery modules plugged into it

- CMS Week

- 16 March 2005

**Notes:**
Error analysis and reliability analysis opportunities across many components
Want to quickly arrive at an accurately diagnosis and treatment that you have confident in
Discover software bugs that only occur once every few hours or on

## Comments (continued)

- The product can lead to better or increased
- System uptime by compensating for problems or predicting them
- instead of pausing or stopping the experiment
- Resource utilization
- the system will use resources that it needs
- Understanding of the operating characteristics of the software
- Ability to debug and diagnose difficult problems

- CMS Week

- 16 March 2005

**Notes:**
Error analysis and reliability analysis opportunities across many components
Want to quickly arrive at an accurately diagnosis and treatment that you have confident in
Discover software bugs that only occur once every few hours or on

## Further Information

- General information about RTES
- www-btev.fnal.gov/public/hep/detector/rtes/
- General information about BTeV
- www-btev.fnal.gov/
- Information about GME and the Vanderbilt ISIS group
- www.isis.vanderbilt.edu/

- CMS Week

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## Further Information (continued)

- Information about ARMOR technology
- www.crhc.uiuc.edu/DEPEND/projectsARMORs.htm
- Talks from our workshops
- false2002.vanderbilt.edu/
- www.ecs.syr.edu/faculty/oh/FALSE2005/
- Wiki (internal, today)
- whcdf03.fnal.gov/BTeV-wiki/DemoSystem2004
- Elvin publish/subscribe networking
- www.mantara.com

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## Slide 28

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## Backup Slides

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## The Problem

*Chapter 9 & Appendix E of the CMS DAQ/HLT TDR provide an excellent description.*
- Monitoring, Fault Tolerance/Mitigation are crucial
- In a cluster of this size, processes and daemons are constantly hanging/failing, becoming corrupted, etc.
- Software reliability & performance depends on
- Physics detector-machine performance
- Program testing procedures, implementation, and design quality
- Behavior of the electronics (front-end and within the trigger)
- Hardware failures will occur!
- one to a few per week... maybe more?

- CMS Week

- 16 March 2005

**Notes:**
Complexity of the event and noise, missing channels, aliasing, etc.

## ARMOR System: Basic Configuration

- CMS Week

- 16 March 2005

## ARMOR: Internal Structure

- CMS Week

- 16 March 2005

**Notes:**
Mention element collection dictates what recoveries are possible (reconfigurable by changing elements)
Attached ARMOR performs a specialized function
Message routing bus
Simple hierarchy shown, lower level has
  reporting/sensing -> detection/analysis -> recovery action sequence elements

## The Demonstration System Components

- Matlab as GUI engine
- GUI defined by GME models
- Elvin publish/subscribe networking (everywhere)
- Messages defined by GME models
- RunControl (RC) state machines
- Defined by GME models
- ARMORs
- Custom elements defined by GME models
- FilterApp, DataSource
- Actual physics trigger code
- File-reader supplies physics/simulation data to the FilterApp
- Demo “faults” encoded onto Source-Worker data messages for execution on the Worker

- CMS Week

- 16 March 2005