Application Programs and Systems - Heterogeneous Multicore Processor Technologies for Embedded Systems - page 195

sends the “SIGINT” signal, which is an interrupt from a keyboard, to a process
specified by the [PID]. That [PID] is obtained through the subsequent commands
between the symbols ` and `. The “ps a” command outputs line by line the status of
processes of all the users. The “grep 'penguin 0'” extracts any line that matches
'penguin 0.' The “grep -v grep” command removes any line that matches “grep.”
The “awk '{print $1}'” extracts the first word of the filtered line in order to get the
PID of the “./penguin 0/dev/fb0” process. After killing a process, the load balancer
of a less busy CPU might pull one or more processes from the busiest CPU. Line 1002
waits for 1 s. Line 1003 kills the penguin drawing sub-application process named
“1.” After killing a process, the load balancer of a less busy CPU might pull one or
more processes from the busiest CPU. Line 1004 waits for 1 s. Finally, no penguin
images remain on the display. That process is one routine of the application program.
The same routine is repeated again and again until the power is turned off.
Figure 6.24 illustrates the time when the number of penguins has increased
from three to four. The number of penguins on the four CPU cores is initially
unbalanced, and penguins are equally distributed among four sections after a while.
Even when the number of penguins decreases from five to four, the number of
penguins in each section is balanced among the four sections as shown in the same
figure, although the names of the penguins are not the same. In this process, we
were able to verify that the load balancing mechanism of the Linux kernel works
fine with the four CPU cores.

6.3.2 Power Management on RP-2

6.3.2.1 Introduction

The second application program has been designed to instantiate the power man-
agement capabilities of the RP-2 chip and RP-2 Linux and to visualize the power
consumption and performance of the system. The RP-2 has two capabilities that
support power saving. One is dynamic voltage and frequency scaling (DVFS), and
the other is power gating. The DVFS of the RP-2 allows each CPU core to change
the frequency independently and allows the whole chip to change the voltage to one
of three voltage sources. The voltage supplied to the whole chip is determined by
the highest frequency of all the CPU cores on the chip as indicated in Table 6.4 .
The power gating of the RP-2 chip allows each CPU core to turn off or on the
power supplied to the core. Each CPU is inside an independent power domain. The
power supplied to a CPU core can be turned off either by itself or by another CPU
core through manipulation of a memory-mapped register. The power supplied to a
CPU core can be turned on either by an interrupt to the CPU core or by another CPU
core also by manipulating the memory-mapped register.
The RP-2 has two clusters each of which consists of four CPU cores. The four
CPU cores are cache coherent within a cluster. The SMP Linux kernel works on
only one cluster with each operand cache turned on. We have used only one cluster
in the application program.