Linux Kernel 4.9 and a (not so) happy Jornada 720

Just saw about this awesome news, well done Stefan! Going to give this a go on my J720.

BTW I think mounting the rootfs on a CF as ext4 is not such a good idea, you will waste CPU cycles with journaling but a bigger problem is it isn't good for the limited write cycles on a CF card. ext2 should be OK I think, I will try it. Update: works fine, just gives a warning at boot.

Edited by munchausen 2021-01-03 2:01 PM

I have found that CF cards are not really required...an SD card placed in a cf adapter works very well. Further partition one can be FAT 32 and at least 15 GB (haven't tried anything larger)...so your J720 can access a winCE hp backup file kept there to easily "dual boot" back and restore to your prior WinCE os/session. Would less journaling cycles speed up rendering any? I guess I will have to compare the two...ext4 vs ext2.

and I agree...Stefan has done an amazing job!

Edited by joval 2021-01-04 2:48 AM

ntware:

I can't imagine how you figured this all out especially the eth0 requirements...but IT WORKS great on WEP for ssh/x11 into RasPi! It only seems a little slower than using a wired ethernet NE 2000 compatible connection.

I haven't taken on the wpa_supplicant wifi option yet...that's coming next. But it is very nice to have the J720 completely free of any ethernet ribbon cable/tether and still fairly snappy rendering web pages (haven't tried youtube videos yet...). Thanks again for all your many efforts...ntware...and all the rest of you!

By default journaling adds information to the journal every time you access a file - even if you're just reading it and not making any changes! The effect is that the jornada CPU has to spend time doing these writes and computing what to put in the journal when it could be doing real work, the PCMCIA(/CF) bus has to do some extra writes which takes up time and bus bandwidth when they could be doing actually necessary disc IO, and the flash card (compact flash, SD card, it doesn't matter) is getting written to all the time for no real reason, which will eventually kill it. The extra writes are a significant overhead: A 2018 paper [1] says that with journaling ext4 does 2.7 times more writes than without, which will slow the system down and burn out flash faster, and this does not include time spent reading the journal or any extra processing for the CPU that is also bogging down the system. Perhaps ext4 without journaling is a better option than ext2 though.

The swappiness should also be turned right down for the same reason; using the swap file on flash will kill it in the end (and is also slow), so the swappiness should be set to tell the kernel to use it only as a last resort. Ideally the swap would be on another card completely, but that isn't an option if you want a network card too.

[1] https://csyhua.github.io/csyhua/hua-tc2018-journaling.pdf

Interesting infos about the file systems!
Would be interesting to do some sort of benchmark.

Regarding swap, I dont worry about the CF card, because there should be enough writy cycles to outlive the Jornada. Remember to have enough free space on the card. Then the wear leveling mechanism can do its magic.
I use several CF/SD cards in systems that have done a lot of write cycles and havent had a single failure in all these years.
But it is always good to reduce swapping, because it is slow. On the Jornada with only 32 or 64 and even with 128MB ram this is not an easy task. If you reduce swapping too much, the OOM killer runs very often.

Stefan

I have killed a CF once, I still have it (Kingston, 16GB). I did it by installing windows 98 on it inside a vaio C1. I think 98 just thrashed the disk until it died. It was new when installed as well! But in any case, I think the performance overhead of a journal is a bad idea for a jornada.

Right you are...using ext2 format does speed up response...and the root delay=5 isn't necessary on boot. How well things will go if system crashes unknown given no jornalling with ext2...but Munchausen (you can take another dose of the strong stuff...given the meaning of your name)...so far seems like a great suggestion just from the speed gain!!!!

I'm using an Aironet 340 wifi card via a wifi extender set to wep on one side and wpa2 on the internet side. It is working great...almost no delay writing this post letter by letter. The J720 completely untethered via wifi to RasPi. It's fast for 200MHz cpu.(getting a little help from my friend the RasPi).

Gonna checkout youtube now. Thanks again...you guys are super IMHO!!

Hi Stefan,

Any luck with the Ambicom card and WPA ?

Thanks,

Mark

No sir. I have to say I hate this card... Nothing works as expected.

Let you know if I make some progress...

Stefan

Thanks for letting me know...

Will think positive for making progress....

Mark

I finally got this working, turns out my file system somehow got damaged, I can now run sudo and other commands that were failing and start X (but touchscreen is not properly calibrated and I don't know how to calibrate it on Devuan).