Smörgåsbord

Last night my Sheevaplug’s power supply unit blew up. Slept clean through it but I think the fumes were responsible for the unorthodox dreaming I did that night. Incidentally, the dream was about electronics. I dreamt I was part of some development project, bringing electronics to the Indian countryside and I had just invented this incredibly tiny airplane which could be made from readily available components such as tins and shrubs. It could fly a route autonomously (!) and had a cargo net which could be used for transporting lumber, cattle, children – anything a farmer family would need transported. The size of a large model airplane, one was supposed to hold on to its landing gear (with one’s legs taking over landing gear functions – better bring some bandages) and enjoy the flight. So I was flying around the hot Indian plains, soldering iron tucked under my belt, spreading the tale of this quantum leap in mobility in the land of Vishnu and Sheeva.

Back to my Sheevaplug. It was no more. A capacitator in the power supply unit (that converts 230VAC to 5VDC) had made a complete mess of itself. And the rest of the PSU. It looks like burnt Marshmallows but smells worse.
Also, the button cell that keeps the system clock running when power is lost, had swollen to unhealthy dimensions and had barfed its contents over part of the mainboard:

Well, at least I’m not alone in getting the marshmallow treatment. It appears to be a heat issue on the first version of the development kit.

Amazingly, the PSU still supplied about 2V, enough to make the blue LED blink to signal me that my marshmallows were ready.

I keep this box with old AC/DC adapters around. I’ve adapted my Sheevaplug to contain a socket to plug in a jack from an external 5VDC 2A supply, replaced the CMOS battery, and after some initial problems with the unit losing track of time after being powered down, all is working fine again. But better not take this Sheevaplug to the scorching heat of the land of Sheeva.

Some quick numbers for those looking for performance figures on the CESA crypto accelerator. Like I was, since my SheevaPlug has one. From the kernel config:

CRYPTO_DEV_MV_CESA
This driver allows you to utilize the Cryptographic Engines and Security Accelerator (CESA) which can be found on the Marvell Orion and Kirkwood SoCs, such as QNAP’s TS-209.
Currently the driver supports AES in ECB and CBC mode without DMA.

Whether the accelerator will be used depends on whether an application uses the in-kernel crypto algorithms. OpenSSL does not unless it is explicitly enabled to use a certain accelerator, such as is the case with the Via Padlock engine. So this particular engine won’t let your SSH run faster. But it will speed up device mapper crypto if you use an AES cipher.

Right, let’s get on with it.

#uname -a
Linux sheeva 2.6.32-gentoo-r3 #3 Thu Feb 4 23:02:42 CET 2010 armv5tel Feroceon 88FR131 rev 1 (v5l) Marvell SheevaPlug Reference Board GNU/Linux


Quick & oh-so-dirty way of getting a RAM-backed block device (that is, if you don’t have swap enabled):

#mount -t tmpfs tmpfs /mnt/tmp/
#dd if=/dev/zero of=/mnt/tmp/blob bs=1M count=224
#losetup /dev/loop0 /mnt/tmp/blob
#cryptsetup -c aes -h sha1 -d /dev/urandom create test /dev/loop0

First we test without CESA.

#dd if=/dev/zero of=/dev/mapper/test bs=1M count=224
234881024 bytes (235 MB) copied, 41.858 s, 5.6 MB/s

Only 5.6 MB/s and the [kcryptd] kernel process is having your CPU for lunch.
Enter CESA:

#dmsetup remove test
#modprobe mv_cesa
#cryptsetup -c aes -h sha1 -d /dev/urandom create test /dev/loop0
#dd if=/dev/zero of=/dev/mapper/test bs=1M count=224
234881024 bytes (235 MB) copied, 18.0525 s, 13.0 MB/s

13.0 MB/s and there’s a new kernel process, [mv_crypto]. It’s eating about three times as much CPU as [kcryptd]. That means it’s offloading, which is good. The results are consistent over time so let’s say there’s a 2.5-fold performance gain.
The loop device setup causes some overhead. Out in the wild you’ll get about 19 MB/s writing to USB HDD. Cheers!