Software Environments - Heterogeneous Multicore Processor Technologies for Embedded Systems - page 159

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Idle Reduction
ondemand
conservative
powersave
performance

40

20

0

0 50 100 150 200

Elapsed Time [s]

Fig. 5.4 Elapsed time and energy consumption with mixed loads

Figure 5.4 plots the elapsed time and energy consumption. The graph also shows
the execution time of the RAYTRACE benchmark. Idle reduction shows very good
performance per energy consumption [ 8 ] .

5.1.3 Physical Address Extension

5.1.3.1 Introduction

The heterogeneous multicore RP-X described in Sect. 4.4 has the physical address
extension (AE) feature, which extends its physical address to 40 bits. We have
decided to extend the Linux HIGHMEM framework to support AE on RP-X.

1. Address Extension
Even if a CPU core has only a 32-bit virtual address space, it can access a physi-
cal address space of over 4 GB with the address extension (AE) feature. It enables
use of more than 4 GB of memory without having to modify the application
software.
2. HIGHMEM

Figure 5.5 is an overview of the Linux HIGHMEM framework. In the figure,
direct translation means that H/W translates from a virtual address to a physical
address. Indirect translation means S/W manages address translation, and a vir-
tual address is translated to a physical address on a memory page basis by using
a translation look-aside buffer (TLB).
The HIGHMEM framework separates physical address memory into two
regions: straight mapped memory corresponding to the straight mapped area in a