> On Nov 28, 2019, at 12:52, Peter Eriksson <p...@lysator.liu.se> wrote:
> 
> I’ve been looking into the “kernel looks to be hung at reboot” problem at 
> bit. Adding a lot of printf() calls to the relevant parts it looks like it 
> actually isn’t hung but busy unmounting filesystems (which we have thousands 
> of), flushing disk caches, calling registered callbacks and stuff and 
> sometimes it takes a bit longer than usual - probably due to ZFS having stuff 
> queued up that needs to be written to disk before it finishes…
> 
> Anyway, I’d like to propose that we add some kind of counter/printf() calls 
> in that code area so we can see that things are indeed progressing. However, 
> I’d probably prefer not to print _every_ filesystem (or registered callbacks 
> - a lot of those...) - that generates a lot of output (tried that :-) but 
> something like:
> 
> Unmounting filesystems:
> 1234 done
> (With the "1234 done” updated something like once per second).
> 
> What’s the right/best way to do that from the kernel? In user space I’d just 
> call time(&t) at some convenient points and only print something if “t” has 
> changed. :-)

Can you use DTrace instead to get the information you need?
Cheers,
-Enji
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