Re: Inquiry: Should we remove "isolcpus= kernel boot option? (mayhave realtime uses)

[Max Krasnyanskiy]

> > I would really appreciate some way to keep the kernel from using 
> > a CPU at all to do fault isolation. If possible not even booting it.
> How does isolcpu= boot option helps in this case ?
> I suppose the closes option is maxcpus=. We can probably add ignorecpus= or
> something to handle your use case but it has nothing to do with isolcpus=.

btw Ingo, I just realized that maxcpu= option is exactly what you need.
Here is how you can use it.
Boot your system with maxcpus=1. That way the kernel will only bring up 
processor 0. I'm assuming cpu0 is "good" otherwise your system is totally 
busted :). Other cpus will stay off-line and will not be initialized.
Then once the system boots you can selectively bring "good" processors online 
by doing
	echo 1 > /sys/devices/system/cpu/cpuN/online

This actually solves the case you're talking about (ie ignoring bad 
processors) instead of partially covering it with isolcpus=.

Dimitri, you can probably use that too. ie Boot the thing with most CPUs 
offline and then bring them online. That way you'll know for sure that no 
timers, works, hard-/soft-irqs, etc are running on them.

So I expect two ACKs for isolcpu= removal from both of you, in bold please :)

Max
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