System information

9 Benchmarks and Verification
This chapter details the performance of the functional units of the CHARM card. Espe-
cially, the throughput and the frame rate of the VGA card implementation are presented.
Previously, two running operating systems are inspected for VGA accesses to get an esti-
mation of the required performance of the CHARM card. Additionally, the throughput of
the emulated USB mass storage device is discussed and finally the power consumption of
the CHARM is examined.
9.1 VGA Function Performance
One of the most important issues of the usability of remote access tools is the frame rate
of the exported screen. The display content should be provided in realtime to interact with
the remote computer. Frame rates of 15 Hz should be sufficient to saturate the human
visual system [103]. The performance of VGA processing, PCI interface and VNC server
form the frame rate of the exported screen. Figure 9.1 shows the processing queue of the
VGA function of the CHARM and the relevant performance parameters of every specific
step. The PCI throughput and the VGA processing time are discussed in section 9.1.2 and
9.1.3. Section 9.1.4 examines the update rate of the VNC framebuffer and the resulting
frame rate.
Host
CPU
VNC
Client
PCI
Interface
VGA
Driver
VNC
Server
PCI
Throughput
VGA
Processing Time
VNC
Frame Rate
VNC
Update Rate
Figure 9.1: VGA processing queue.
In this process, the performance of the PCI interface limits the throughput of the incoming
and outgoing VGA data. Furthermore, the throughput of a VGA card can influence the
system performance of the computer. If the graphic card cannot achieve the data traffic, the
computer system has to stop the graphical output. Single-threaded software with graphical
output has to wait for the graphic card. To get a guideline value of the expected VGA data
traffic, the graphical output of two operating systems were inspected. The following section
discusses the performance requirements of a VGA card.
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