Raspberry Pi 1 and 2 compared

SCP Performance Test

The secure copy protocol (SCP) provides for secure transfer of data over the Internet. The transfer involves two processes: an SSH daemon and an SFTP server. In operation, an SSH daemon acts like the eye of a sewing needle because encrypting and then delivering data into the network places a heavy burden on the CPU. The SSH daemon uses about 90 percent of the capacity of the CPU on a Rasp Pi when transferring with SCP. The SFTP server then has to be satisfied with the remaining 10 percent (Figure 5).

Figure 5: Transferring data over the network using SCP quickly utilizes all of the computing resources of the Raspberry Pi.

Both of theses processes run inside the lone CPU core on the first generation Rasp Pi. The second generation Rasp Pi makes a CPU core available to each service exclusively. This makes it possible to demonstrate the difference in performance (Table 2). During the course of the test, the system writes data to a RAM disk in memory to avoid results that might be influenced by the performance of the SD card and its connection.

Table 2

SCP Benchmark Results

Frequency (MHz)

 

SCP Writing1

SCP Reading1

ARM

SDRAM

GPU Core

Temp. (°C)

Mbps

%

Mbps

%

Raspberry Pi 2, Raspbian

900

450

250

53.5

52.6

100.0

54.8

100

1,000

500

500

58.4

56.3

107.0

69.0

126

1,050

500

500

58.4

65.6

124.6

69.0

126

1,1002

500

500

Raspberry Pi 1, Raspbian

700

400

250

43.3

21.1

 40.0

21.1

 38

1,000

600

250

51.4

36.4

 69.1

33.3

 61

Raspberry Pi 2, Debian Jessie3

900

450

250

 

47.6

 90.5

52.6

 96

1,050

500

500

 

58.0

110.1

71.4

130

1Average of several passes.

2Could not execute test because of RPi2B instability.

3Version with packages optimized for ARMv7.

The biggest difference between the generations appears without overclocking the SoCs. The new Rasp Pi pushes data through the network at a speed 2.5 times greater than that achieved by the first generation Rasp Pi. The RPi2B with Debian Jessie [8] is a surprise, with a slightly lower data rate compared with Raspbian.

Overclocking the new Rasp Pi to 1.05GHz teases out more than 25 percent additional performance. A part of this performance can probably be attributed to the 10 percent higher clock rate of the working memory, as well as the higher clock rate for the GPU core that drives the L2 cache.

In an SCP test, an optimally overclocked RPi2B at 70Mbps achieves a transfer rate that is more than twice as high as a fully overclocked RPi1 at 33Mbps. However, even the "turbo charged" RPi2B cannot achieve the theoretically maximum bandwidth of a 100Mbps LAN port, which is about 90Mbps.

Theoretically, the maximum possible clock rate is 1.1GHz, but it was not possible to get reliable operation of the hardware used in the test at that rate. Instead, crashes and errors prevented the measurement of the transfer rate. It might be possible to achieve stable operation even with an overclocked CPU by fine tuning the excess voltage and the clock rates of the RAM and the GPU core.

Practical Experience

A nice detail greets the Raspbian user when the RPi2B starts up. Four raspberries – one for one core – decorate the screen. One big difference between the two generations becomes apparent as soon as the desktop environment loads and the individual programs start. The single-core Pi was constantly pushed to its limits and needed regular timeouts. The RPi2B ran smoothly and the individual applications started quickly. The four processor cores run simultaneously and often use less than 10 percent of their cumulative capacity.

This improved performance makes for a fun experience surfing the web. Websites load quickly, and in the time it takes the RPi2B to complete a full rendering, the RPi1 is still showing a white page. The Epiphany browser has been able to play YouTube videos for some time thanks to the work of the Foundation, and the YouTube page works at an acceptable speed on the RPi2B.

The SunSpider benchmark, which is used to measure browser speed on dynamic websites, indicates that the RPi2B achieves results at least five times faster than the RPi1 [9]. Complex web applications (e.g., Google Docs) profit from this increase in performance. Google Office runs smoothly on the new Rasp Pi; however, in some places its performance still cannot compare to that of a full-sized computer.

On the other hand, LibreOffice, Calc, Writer, and Impress all run at a comfortable speed on the RPi2B. Wait times only occur when complex macros and plugins are executed. Significant improvements become clear when Gimp, the graphics and painting program, is used. Although it is possible to start this program on the RPi1, each action runs as if in slow motion.

An unofficial preview of Debian Jessie has a surprisingly short boot time thanks to Systemd. The login prompt appears as soon as the Rasp Pi is connected. This definitely makes Debian interesting for users that start up their Rasp Pi only as needed when it is in battery mode.

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