Uwatec Smart Z data download takes 1.5 hours for only 4 dives

[Jef Driesen]

On 29-12-13 23:32, Linus Torvalds wrote:
> On Sun, Dec 29, 2013 at 6:39 AM, Sape Sikkema <s.sikkema at telfort.nl> wrote:
>>
>> Indeed, the dongle is a SigmaTel STIr 4200, its ID is 066f:4200. It did not
>> come with the dive computer. It was a $5.00 purchase from a webshop in
>> Hongkong.
>
> While I don't have a dongle or target yet, mind trying a few things?
>
> If you can recompile your kernel with CONFIG_HZ set to just 100, that
> would be interesting to see. The STIR4200 driver ends up doing busy
> loops for some delays *if* those busy loops are shorter than one
> kernel tick, and that means that the exact setting of CONFIG_HZ can
> matter.
>
> There have been basically no changes to that driver in the last
> several years (all of the current git history), but the slowdowns can
> obviously come from unrelated infrastructure changes (like, for
> example, that timeout handling change due to HZ changes). So..

It used to be possible to attach the irda subsystem to a pty. I successfully 
used this setup for testing libdivecomputer (see bottom) without needing any 
irda hardware:

http://www.libdivecomputer.org/simulator.html

This might be a way to reproduce the slowness without needing the hardware. 
Assuming the problem is in the irda subsystem and not the stir4200 driver of 
course.

Unfortunately, this suddenly stopped working a few years ago (kernel panic if I 
remember correctly), and I haven't tried it again recently. But maybe it works 
again on recent kernels?

Jef