[Server-devel] Best XSCE strategy for us in Pacific with XO-1.5 2GB Testing XSCE 3 on XO 1.5 2GB os855

[James Cameron]

On Thu, Jun 20, 2013 at 06:03:37AM +1100, David Leeming wrote:
> Finally, is there any performance penalty for running it from the
> external SD card?

It would depend on the card, which as you know contains a small
controller with firmware that is closed to you.

Read performance is fundamental to system performance.  Read
performance is constrained by the device, the method by which it is
attached, and the memory bandwidth.

You can measure read performance for both using what you have now:

- boot the system and get a root terminal prompt,

- ensure the system is idle, not doing anything unusual,

- identify the name of each device:

  # cat /proc/partitions
  major minor  #blocks  name
  
   179        0    7766016 mmcblk0
   179        1      65536 mmcblk0p1
   179        2    7696384 mmcblk0p2
   179       16       2048 mmcblk0boot1
   179        8       2048 mmcblk0boot0
   179       24    3858432 mmcblk1
   179       25    3857408 mmcblk1p1

  (in this example from an XO-4, the internal eMMC device is mmcblk0,
  and the external SD card is mmcblk1, but this won't always be so; on
  your system, with OLPC OS, the device it booted from will be
  mmcblk0, the other device will be mmcblk1)

- make a measurement of read performance of the external SD card,

  # dd if=/dev/mmcblk0 of=/dev/null bs=2M count=1000
  1000+0 records in
  1000+0 records out
  2097152000 bytes (2.1 GB) copied, 37.7448 s, 55.6 MB/s

- make a measurement of read performance of the internal microSD card,

  # dd if=/dev/mmcblk1 of=/dev/null bs=2M count=1000
  1000+0 records in
  1000+0 records out
  2097152000 bytes (2.1 GB) copied, 131.57 s, 15.9 MB/s

  (the size is chosen to be larger than the memory of the system).

- repeat the measurements a few times in case there are activities
  that are affecting the result,

- record the measurements for later comparison, so that you can detect
  a regression.


There are also other important measurements, such as a write
performance, but you need other tools for that.  Let me know if you
need that.  Write performance degrades over the lifetime of a Flash
storage product.

(The results above show the XO-4 internal eMMC achieved 56 MB/s, and
the external SD card achieved 16 MB/s).

-- 
James Cameron
http://quozl.linux.org.au/