efficient execution of mixed application workloads in a hard real-time multicore system

Marco PaolieriRePP WorkshopOctober 15th

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Efficient Execution of Mixed Application Workloads

in a Hard Real-Time Multicore System

Marco Paolieri (BSC/UPC)

Eduardo Quiñones (BSC)

Francisco J. Cazorla (BSC)

Mateo Valero (BSC/UPC)

RePP WorkshopGrenoble, 15th October


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Future Real-Time Systems

Current real-time embedded systems require higher performance than provided by current processors

Increasing safety, comfort, number and quality of services


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Architecture

What about predictability?What about predictability?


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Multicores in RTESs: disadvantages

It is harder to perform WCET analysis for multicore processors than for single-core because of Inter-thread Interferences

Inter-thread interferences accessing shared resources make the execution time vary

Execution time, and so the WCET of a HRT depend on the mixed application workload

WCETa d

Where:

• WCETa WCET est without interferences

• d deadline

• ETa,b ET of a running with b

• ETa,c ET of a running with c

ETa,b ETa,c

deadlinemiss

Is it possible to use multicores to execute mixed application workloads?

Is it possible to use multicores to execute mixed application workloads?


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Our Goal

Execute efficiently mixed application workload providing

predictability to HRTs

maximizing performance of NHRTs with the resources not used by HRTs


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Regarding HRTs

Our multicore architecture guarantees by design that the maximum delay a request accessing a shared resource may suffer due to inter-thread interferences has an Upper Bound Delay (UBD)

Inter-thread interferences < UBD

Round Robin provides UBD based on the number of requestors

UBD = (NHRT – 1) * LBUS

where LBUS is the latency of the bus and NHRT the total number of HRTs running at the same time

The impact of inter-thread interferences on WCET is up to 40% [Paolieri et al. Hardware Support for WCET Analysis of Multicore Hard Real-Time Systems, ISCA’09]


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What about Non Real-Time Tasks?

HRTs are accessing shared resources as soon as they are available, what we call Average-Case Resource Managament (AC-RM)

NHRTs could be starving before accessing shared resources

To execute efficiently a mixed application workload

It is required to maximize the perfomance of NHRTs


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Our Proposal

No advantages if executing the HRTs before their WCET

We evaluate a resource management policy, called Worst-Case Resource Management (WC-RM)

Every access to a shared resource from a HRT is stalled by UBD cycles

This forces HRTs to be executed closer to their WCET

It provides performance to NHRTs still guaranteeing that HRTs meet their deadlines

Reducing the variance between average case execution time and WCET performances of NHRTs can increase


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How It Works

1.041.011.031.061.051.051.041.051.061.051.04


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Experimental Setup

As HRT benchmarks we use:

A real HRT application provided by Honeywell

3D collision avoidance algorithm

EEMBC Automotive

As NHRT benchmarks we use

MediaBench, MiBench, SPEC CPU 2006


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Results

Baseline: throughput of NHRTs using the AC-RM

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Effect on HRTs

Baseline: Performance of HRTs using AC-RM

WC-RM is between 1 and 2 % close to its WCET estimation

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Conclusions

Our architecture is designed from a WCET point of view

It implements a hardware shared-resource management policy, called Worst-Case Resource Management (WC-RM)

It improves the performance level of NHRTs when running in a mixed application workload


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Thanks for the attention!

efficient execution of mixed application workloads in a hard real-time multicore system

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