ath79: move 8/32 boards to tiny subtarget

[David Bauer]

Hello Sven,

On 9/18/20 1:27 AM, Sven Roederer wrote:
> Adrian, David,
> 
> Am Mittwoch, 16. September 2020, 16:15:42 CEST schrieb David Bauer:
>> Hi,
>>
>> On 9/16/20 11:40 AM, Adrian Schmutzler wrote:
>>>> -----Original Message-----
>>>> From: openwrt-devel [mailto:openwrt-devel-bounces at lists.openwrt.org]
>>>> On Behalf Of Sven Roederer
>>>> Sent: Mittwoch, 16. September 2020 09:17
>>>> To: openwrt-devel at lists.openwrt.org
>>>> Subject: ath79: move 8/32 boards to tiny subtarget
>>>>
>>>> Hi,
>>>>
>>>> not sure if this has been discussed before.
>>>> I recently worked with some 8/32 boards (Ubiquiti Nanostation M (XM),
>>>> TPLink
>>>> WR842 v2)  for our Freifunk-project and realized that the low RAM
>>>> situation
>>>> requires quite different handling than the full boards (8+/64+).
>>>>
>>>> I wonder if there is a reason to not move the boards, which are affected
>>>> by
>>>> the 4/32MB warning also, to the ath79-tiny target?
>>>
>>> I wonder whether the tiny subtarget will actually make much difference for
>>> RAM issues?
> 
> My idea based on the fact, to have an easy way to disable certain kernel-
> features to reduce teh kernel-size (in flash and RAM). Candidates I see here 
> are: USB-Support, additional filesystems, block-devices, ...
> Even some devices provide USB-connectors it might be better to have less OOM-
> crashes and reboots than installing a usb-flashdrive. In our Freifunk-Firmware 
> I've seen much less runtime-problems with a stripped down kernel.
> With having the 8/32 in tiny it would just be a config-file for the low-RAM 
> boards. Having them in generic subtarget would require to build 2 kernels for 
> the same subtarget.
> 
>> In it's current state, it will most likely increase low-memory issues as the
>> squashfs blocksize is 1024kB compared to the regular 256kB. Not that
>> ath79-tiny has no target-flag for small memory set.
>>
> 
> Did you miss an "e" ? "Note that ath79-tiny has ..." gives more sense to me. 
> Reading it this way, you expect the larger blocksize was choosen as tradeoff 
> between using the flash most efficient vs. RAM for the 4/32 boards?
> I've seen there is a low_mem flag for some 16MB boards defined. It seems that 
> for some config-options SMALL_FLASH and LOW-MEM are conflicting.

Yes, there was an e missing.

We've experienced severe system instabilities with larger blocksizes (the default
one for ar71xx-tiny to be precise) downstream. [0] [1]

However, In my opinion the blocksize upstream works well for people looking for a
home router, as memory consumption is typically lower and some additional space
is desirable there.

I could also imagine the low-mem target feature and It's configuration implications
have to be assessed as a whole, given it did not experience much use for a longer
period of time.

[0] https://github.com/freifunk-gluon/gluon/issues/2032
[1] https://github.com/freifunk-gluon/gluon/commit/7e8af99cf504ca1dc389f282a0c94f4a911571be

Best wishes
David

> 
> Sven
> 
> 
>