A bit-accurate power estimation simulator for NoCs
Erwan Moréac, Pierre Bomel, Johann Laurent et André Rossi*
Lab-STICC, Université de Bretagne Sud, Lorient, France
* LERIA, Université d’Angers, Angers, France,
Abstract—We have developed an enhanced version of Noxim
(Noxim-XT) to estimate the energy consumption of a NoC in a SOC.
Noxim-XT is used in a two-step methodology. First, applications are
mapped on a SoC and their traffics are extracted by simulation with
MPSOcBench. Second, Noxim-XT tests various hardware
configurations of the NoC, and for each configuration, the
application's traffic is re-injected and replayed. An accurate
performance and power breakdown is provided, and the user can
choose different data coding strategies. With the help of Noxim XT,
each configuration is bit-accurately estimated in terms of energy
consumption. After simulation, a spatial mapping of the energy
consumption is provided and highlights the hot-spots. Moreover, new
coding strategies allow for significant energy savings. Noxim XT
simulations and a FPGA-based prototype of a new coding strategy
will be demonstrated at the U-booth to illustrate our results.
The motivation of these works rely on the fact that today’s
complex many-cores and SoCs contain one (if not several)
NoCs, and NoC power consumption can represent a significant
proportion (40%) of the overall power consumption. These
works faced challenges and raised several questions.
First, estimate NoC power consumption at system-level,
and bit-accurately, without the need for electrical simulations.
"Is it possible to shorten the simulation times and still get
good enough estimations?"
Second, design and test new coding strategies to reduce
power consumption on links.
"What is the energy impact at system-level?"
"Is a single coding strategy always the best fit?"
"What is a good set of coding strategies?"
Third and last, explore the design space of these new
coding strategies.
"Is it realistic in terms of simulation time and precision?
Fig. 1 – Energy estimation flow
Fig. 2 – Hot spots location
The main ideas are the following (Fig. 1)
i) Enhance Noxim simulator and modify it to add a
crosstalk-aware link power model moving towards better
power estimation. This new version is called Noxim-XT.
ii) Use a SoC simulator to extract application traffics. The
selected simulator is MPSoCBench. Allow this simulator to run
application based traffics including packets content. This new
version is called Noxim-XT.
iii) Design new coding strategies, that can optionally use
NoC’s feedback. New coding styles (parallel, parsimonious,
temporal shielding), and new selection strategies have been
designed and compared.
iv) Simulate with Noxim-XT to estimate and extract power
consumption. Check that application behavior is correct with
various application traffics, coding styles, and selection
strategies.
Fig. 3 – Power consumption reports
Conclusion: depending on the application, the coding style and
the selection strategy, energy savings can be up to 35% of the
overall NoC energy consumption.