Avian’s Blog

In my experience, slow filesystem I/O is one of the biggest disadvantages of cheap ARM-based single-board computers. It contributes a lot to the general feeling of sluggishness when you work interactively with such systems. Of course, for many applications you might not care much about the filesystem after booting. It all depends on what you want to use the computer for. But it's very rare to see one of these small ARMs that would not be several times slower than a 10-year old Intel x86 box as far as I/O is concerned.

A while ago I did some benchmarking of the eMMC flash on the old Raspberry Pi Compute Module. I compared it with the SD card performance on Raspberry Pi Zero and the SATA drive on a CubieTruck. In the mean time, the project that brought the Computer Module on my desk back then has pivoted to a BeagleCore module. Since I now have a small working system with the BCM1 I thought I might do the same thing and compare its I/O performance with the other systems I tested earlier.

The BCM1 is a small Linux-running computer that comes in the form of a surface-mount hybrid module. It is built around a Texas Instruments AM335x Sitara system-on-chip with a single-core 1 GHz ARM Cortex-A8 CPU. The module comes with 512 MB RAM and 4 GB eMMC chip. It is supported by the software from the BeagleBoard ecosystem and in my case runs Debian Jessie with the 4.4.30-ti-r64 Linux kernel. Our board has a micro SD card socket, so I was also able to benchmark the SD card as well as the eMMC flash. I was using the Samsung EVO+ 32 GB card.

To perform the benchmark I used the same script on BCM1 as I used in my previous tests. I used hdparm and dd to estimate uncached and cached read and write throughputs. I ran each test 5 times and used the best result.

The write performance is better with the SD card than the eMMC flash on BCM1. SD card on BCM1 is also faster than the SD card on Raspberry Pi Zero, although this is probably not relevant. It's likely that the Zero performance was limited by the no-name SD card that came with it. eMMC on the BCM1 is slower than on Raspberry Pi CM.

The 16.2 MB/s result for the SD card here is somewhat suspect however. After several repeats, the first run of five was always the fastest, with the later runs only yielding around 12 MB/s. It is as if some caching was involved (even though fdatasync was specified with dd).

Interestingly, things turn around with read performance. BCM1's eMMC flash is better at reading data than the SD card. In fact, BCM1 eMMC flash reads faster than both Raspberry Pi setups I tested. It is still at least 3 times slower than a SATA drive on the CubieTruck.

Cached read performance is the least interesting of these tests. It's more or less the benchmark of the CPU memory access rather than anything related to the storage devices. Hence both BCM1 results are more or less identical. Interestingly, BCM1 with the 1 GHz CPU does not seem to be significantly better than the Compute Module with the 700 MHz CPU.

My results for the BCM1 eMMC flash are similar to those published here for the BeagleBone Black. This is expected, since BeagleBone Black has the same hardware as BCM1, and gives me some confidence that my results are at least somewhat correct.