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DOI: 10.4230/LIPIcs.ECRTS.2018.3
URN: urn:nbn:de:0030-drops-90005
URL: http://drops.dagstuhl.de/opus/volltexte/2018/9000/
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Benedicte, Pedro ; Hernandez, Carles ; Abella, Jaume ; Cazorla, Francisco J.

HWP: Hardware Support to Reconcile Cache Energy, Complexity, Performance and WCET Estimates in Multicore Real-Time Systems

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Abstract

High-performance processors have deployed multilevel cache (MLC) systems for decades. In the embedded real-time market, the use of MLC is also on the rise, with processors for future systems in space, railway, avionics and automotive already featuring two or more cache levels. One of the most critical elements for MLC is the write policy that not only affects several key metrics such as performance, WCET estimates, energy/power, and reliability, but also the design of complexity-prone cache coherence protocol and cache reliability solutions. In this paper we make an extensive analysis of existing write policies, namely write-through (WT) and write-back (WB). In the context of the real-time domain, we show that no write policy is superior for all metrics: WT simplifies the design of the coherence and reliability solutions at the cost of performance, WCET, and energy; while WB improves performance and energy results, but complicates cache design. To take the best of each policy, we propose Hybrid Write Policy (HWP) a low-complexity hardware mechanism that reconciles the benefits of WT in terms of simplifying the cache design (e.g. coherence solution) and the benefits of WB in improved average performance and WCET estimates as the pressure on the interconnection network increases. Guaranteed performance results show that HWP scales with core count similar to WB. Likewise, HWP reduces cache energy usage of WT, to levels similar to those of WB. These benefits are obtained while retaining the reduced coherence complexity of WT, in contrast to high coherence costs under WB.

BibTeX - Entry

@InProceedings{benedicte_et_al:LIPIcs:2018:9000,
  author =	{Pedro Benedicte and Carles Hernandez and Jaume Abella and Francisco J. Cazorla},
  title =	{{HWP: Hardware Support to Reconcile Cache Energy, Complexity, Performance and WCET Estimates in Multicore Real-Time Systems}},
  booktitle =	{30th Euromicro Conference on Real-Time Systems (ECRTS 2018)},
  pages =	{3:1--3:22},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-075-0},
  ISSN =	{1868-8969},
  year =	{2018},
  volume =	{106},
  editor =	{Sebastian Altmeyer},
  publisher =	{Schloss Dagstuhl--Leibniz-Zentrum fuer Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{http://drops.dagstuhl.de/opus/volltexte/2018/9000},
  URN =		{urn:nbn:de:0030-drops-90005},
  doi =		{10.4230/LIPIcs.ECRTS.2018.3},
  annote =	{Keywords: multilevel caches, real-time systems, multicores, WCET}
}

Keywords: multilevel caches, real-time systems, multicores, WCET
Seminar: 30th Euromicro Conference on Real-Time Systems (ECRTS 2018)
Issue Date: 2018
Date of publication: 20.06.2018


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