* Dewayne Geraghty <dewa...@heuristicsystems.com.au> [20210416 06:26]: > On 16/04/2021 2:29 am, Felix Palmen wrote: > > Right now, I'm running a test with idprio 0 instead, which still seems > > to have the desired effect, and so far, I didn't have any of these > > stalls. If this persists, the problem is solved for me! > > > > I'd still be curious about what might be the cause, and, what this state > > "zfs tear" actually means. But that's kind of an "academic interest" > > now. > > Most likely your other processes are pre-empting your build, which is > what you want :).
Yes, that's exactly the plan.
> Use /usr/bin/top to see the priority of the processes (ie under the PRI
> column). Using an idprio 22, means (on my 12.2Stable) a PRI of 146. If
> your kern.sched.preempt_thresh is using the default (of 80) then
> processes with a PRI of <80 will preempt (for IO).
I was doing that a lot, that's how I found those "global" I/O stalls
were happening when some processes were in that "zfs tear" state (shown
in top only as "zfs te").
> Even with an idprio 0, the PRI is 124. So I suspect that was more a
> matter of timing (ie good luck).
That seems kind of unlikely because the behavior is pretty reproducible.
Having observed builds on idprio 0 (yes, this results in a priority of
124) for a while, I still see from time to time processes getting
"stuck" for a few seconds, mostly ccache processes, but now in state
"zfsvfs" and the rest of the system is not affected, I/O still works.
So, something did change with ZFS and priorities between 12.2 and 13.0.
Running the whole builds on idprio 22 worked fine on 12.2.
> You could increase your pre-emption threshold for the duration of the
> build, to include your nice value. But... (not really a good idea).
That would clearly defeat the purpose, yes ;)
> Re zfs - sorry, I'm peculiar and don't use it ;)
I suspect the relevant change to be exactly in that context, still
thanks for answering :) Now that I have a working solution, it isn't an
important issue for me any more. Curiosity remains…
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